How to address the disapproval of someones actions when he/she throws litter on the ground

Question

Today I was cycling home from work. I was just cycling past a group of two girls when one of them hit me carelessly when she was throwing her tin can of energy drink on the ground. They said "sorry sir" in a mocking way and started laughing as I cycled past. I didn't care about that the tin can hit me. However, I felt very angry about the impact on society and the environment of their careless actions (throwing a tin can on the ground). A bit later, when we were waiting at the traffic light, I wanted to address my disapproval of their actions. However, I was not able to come up with a statement that seemed effective. They seemed so indifferent towards it, throwing their litter on the ground like they did not care.

Now, after this event, I feel bad about not addressing it. I still can't think of a statement that would make them rethink their actions, and hopefully, act differently next time.

Possibly relevant: Although I'm 22, I look rather young for my age. Although they are definitely younger, they might not see me as an authority.

So, how can I address someone's actions in such an event in a way that at least shows my disapproval, and hopefully makes them never litter again?

Answer 1

Method 1

Suited for when people are likely to be agreeing with you. For Reference

-Strategies

1. Explanation of Purpose: About that soda can on the ground...
2. Complaint: I think you shouldn't do that.
3. Request for Solution: Would you mind to put that can into the bin?
4. Request for non-recurrence: Can you promise not to do that again?

-Phrasing

1. Using pronouns such as "We", to indicate that both parties share the blame and as a way of negotiating the problem: I hope we can come to an understanding.
2. Use of questioning to ask for advice, for permission to explain oneself and/or to get the listener to reconsider or discuss the problem: Could you help me to pick the can up?
3. De-personalization of the problem to transfer blame from the interlocutor to the problem: This can is not where it's supposed to be.
4. Use of mitigators to soften the complaint: I'm a bit annoyed by the fact that...

Ask them to pick up the can with:

"Hey, I don't mind the soda can hitting me. I'm just a bit annoyed by that soda can laying on the ground. Would you be able to pick it up, please?"

Tell them to not litter again:

"I know its not a big deal. But every little act helps the environment, you can try throwing it in the trash can next time."

Method 2

Suited when people are not likely to even consider doing what you suggest.

From the suggestion in the comments, I understand that people might just laugh at the generic answer above. I understand a generic answer might not help.

If littering is against the law in your country.

"Hey, do you know you are committing a crime. You are littering, and its against the law. Please don't do that again, or I'll have to report this!!"

If littering is not against the law in your country.

"Hey stop, what are you doing? Don't you think we have enough litter already?"

Edit: I thank you guys for commenting. I know this answer might not be to your satisfaction. Please do tell if you have any suggestions.