I highlighted the most important parts put took the liberty to add more precision in case you are interested in the "hidden" mechanics.
Littering, parking on pavement and hitting dogs are very different kind of actions.
The examples you brought up are quite broad and don't have a lot to do with each other and I believe that the most significant pattern we can draw between them is :
You are talking about people that put their impulses/short-term convenience before the law or even manners.
That's basically the common trait between the events you describe: You witness people who do what suits them and don't care about the others regarding the issue.
Then, you come, saying them, who are grown-ups, that their conduct is wrong. I don't know how you use to present it, what kind of words and tone you use, but even polite notifications make such people in such a situation to quickly lose their shit.
I'm not saying you are wrong to point it out to someone when they do things they shouldn't, but you shouldn't be surprised that they don't take it very well. Besides, being told what to do by a stranger is a pretty effective way of losing one's nerve.
Do you actually believe that people who litter or park like assholes don't know it's wrong? Do you believe that you are teaching them something they didn't know and making them a favor? They already know it and yet they still did it. Telling them their wrongs is not going to lead to a better situation. Besides, even though I'm not building conclusions regarding your reasons, a lot of people who do that kind of comments are self-righteous pains in the ass. They are people who shout at you in public to point out how their values or whatever are better than yours. May it be true, it's not a reason to shout it at people and expect somehow a satisfying result. It's arrogant, rude and basically feels like : "I have to respect these restraining rules so I'm pissed at you not doing it and will do my best to let everyone know as much I'm better than you for doing it, because it makes me sick that some can not follow these rules and get as much respect as I do.
Not trying to infer stuff about you, I don't know you. Just try to get how people react, put yourself in their shoes. Get along with the fact that you cannot change people you cross on the street.
As a side note, I don't know if it has to do with your mindset or simply your way of writing your question but when I read "I still feel though that he didn't get a lesson." it tastes weird. Don't try to teach lessons to people who do bad things, all you will accomplish is pissing them off. You might even find troubles with either these people or the police enforcement.
TLDR : That's where I answer the main question.
To be honest, I don't see much that you can do about that, except maybe pointing it out while remaining as humble as possible. Let me explain myself :
Regardless of the tone, suddenly speaking to a stranger qualifying their conduct and stating what they should or shouldn't do is confrontational, whether you intend it or not, and surely you intend it, their is nothing to be afraid of with that word. Sure being aggressive and/or assertive is also going to add more weigh to it.
How people feel when treated that way, regardless of whether they feel in ther right or not, is humiliation. That's it. Another grown-up is treating them the way grown-ups treat children : by qualifying their conduct and tell them what they should change regarding it. You are ignoring their adult status, reaping them of it. This may not be your goal, but that doesn't make it less real.
Your main question was How to deal with that kind of person ?.
The main issue being that your current way of dealing with it is met with aggressivity, we should try to solve that particular issue, so lets reword it to How can I point out one's uncivil conduct without that person to feel lectures, therefore reacting violently ?
I invite you to confirm if whether or not that question is a good match with your current concern.
I can only advise you some elements to focus on to be certain that your reaction is as likely as it can be to have the desired effect (and I wanted to make a list somewhere in that answer, also).
Play the thing in your head beforehand, plan what you will say in advance. Simulation allow us to test stuff without having to deal with the costs and consequences of practically making these tests. That's how we refined our understanding of nuclear explosion without blasting too much landscape. Nuclear explosions and confrontations are alike : knowing beforehand that an attempt will be a disaster can do a great deal to you regarding diplomacy.
Stay calm. We tend to mirror the mind states of those around us, especially when they confront us. That's an evolutionary treat that prevents us to be caught off guard if violence steps are crossed. It's also what's responsible for escalation. It can happen that the opposing side gets a step or two higher than us because we stressed them. Remaining calm instead of doing the same breaks the escalation.
Conflict usually allows only two outputs : fight or flight. Escalation usually happens when the fight output is preferred at any iteration of the cycle, whether it's because of pride or because flight is considered impossible. In that case, the escalation can be prevented by incuding a third output that acts as a safety valve, it's usually an alternative flight that doesn't entail pride.
By making such a thing part of your step forward, you make it possible for the other person(s) to be able to walk away from the conflict or ignore it without feeling that they submit to you. That's why societies like Canada or the UK (among many others) are so obsessive about politeness when interacting with (near) strangers. politeness makes the ground neutral by avoiding personal influence. By make it look like it's no big deal, the situation can stay peaceful.
So the two elements there are introducing yourself before coming to the real matter - not by name, just some neutral formal thing to set the encounter before you introduce the hot stuff - and keeping it neutral. That kind of speech is how grown-ups are supposed to talk and can let a lot of sensitive issues being discussed without most people being stressed out and it can be used in a great variety of interpersonal issues.
Then say it only if it feels right to you. If
A typical speech I would use would be something along these lines :
Hi Sir ! Please excuse me, I know you are busy, but I couldn't help
but notice that you parked on a reserved spot. Maybe you didn't notice
or are in a hurry, but since it was one of the last available and that
it add more pain and bother on a disabled person who would come in the
meantime, would you please reconsider your choice to park here ?
That sure can be refined, but the key points are there :
- Introducing the interaction. The words by which you get the person's attention defines how that person will react. If they are violent, it will set the field as a confrontation. If it's polite, you will seem less aggressive and the person won't feel threatened. It's damn important as otherwise, whatever you say after will be heard with angry ears. Bonus point for the respect mark, if you give him some Sir, you are showing respect. excuse me greases the situation : you are letting yourself appearing vulnerable by acting humbly. It can be wasted if the following words are disrespectful - "Excuse me, but you are parked like a d**head*", bad move - but otherwise it gives the other person the initiative so they can stay calm for the moment. Also, by acknowledging that the person might be busy, you are showing that you also value that person's time, which is also important. It implies that you wouldn't intervene if it wasn't important and that you consider the other person as a human being with their own agenda and stuff to do.
- Attesting the issue. You go one step further by throwing a neutral assertion, in that case a quick and objective description of what you saw. You don't put blames, don't make conclusions, just attest. That kind of statement is a good way to continue the introduction of the interaction as it is neutral and still allows you to explain the situation. Make it objective and straight to the point, don't point fingers, don't put blame, just describe. You have no audience to convince you are right, just another person to convince that they did the wrong thing, no need to antagonize them.
- Since you are still implying that the person behaved wrongly, you can come up with possible justifications for their actions that would be valid, as it serves a double purpose. First, you prevent escalation by leaving them a safe exit : they can always answer you "yes, in fact I didn't notice" or "Indeed, I'm in a hurry and won't have for more than five minutes" if they don't want to escalate, that's the safety valve. Second, by forcing yourself to wonder for what valid reasons they might have behaved that way, you force yourself to see them as the human beings with their own life which makes your tone more credible and you calm yourself in the event that it made you mad by realizing that maybe they aren't that bad or that wrong - even if maybe/surely they are.
- Give them a plain and simple reason for them to do otherwise that has nothing to do with you. People won't have the impression of submitting to your biding if you ask them to do it for somebody else, like a potential disabled person.
- Don't ask them to do X. Ask them to reconsider doing it after you exposed them what they did and the reason why it's your opinion that they should have done something else. Children are told to do things. Adults share opinions and let each other do their own choices based on them. By simply asking people to reconsider their course of actions after having - nicely - listen to your opinion, you are also valuing their thinking process and respecting their ability and right to act accordingly.
I hope it can help you with your issue. I know that it takes some practice to apply these guidelines in all situations and I admit that I do myself get confrontational in the heat of the moment only to regret it afterwards, but maybe it can help to know the underlying gears.
If I had only one advice, it would be to always keep in mind that other people are... well... other people... They have their own mind, opinions, background and impulses, just like you and me. Sometimes, all it takes is one to find back their calm to de-escalate something, and that takes more courage than it should.