You seem to find yourself in a situation of sides. Wherein your acquaintance seems to perceive a situation in which it's you vs. them.
Your acquaintance then jumps onto your imaginary side and starts defending it.
However, those actions are based on inaccurate representations of the situation. So really, I think you're looking for a way to change this perception, by using your communication skills to shape what's going on.
I'm going to go through steps in order of severity:
1. Be in on the joke (when appropriate)
You said that sometimes you even find things funny and don't want to be defensive or be defending. Those situations are perfect opportunities. From a US perspective, jokes at other peoples' expenses don't really have to hurt anyone. In fact, when used correctly, they can be enjoyable for even the person they are made "against".
When that happens, and you feel the joke really isn't meant to hurt you, make it visibly clear you enjoy it. Laugh, play along, maybe even counter with your own joke about it.
So someone says:
I didn't mean that literally. Ha, sometimes talking to you feels like talking to a robot.
You can laugh and respond:
Ha, good think us robots will be taking over your job soon.
This playful banter will firstly make sure the situation stays even, and not one-sided. That's important, because it will give off social cues that suggest there is no conflict, and therefore no need to defend anyone.
Also, this technique is sometimes recommended even if the other person is actually being mean, because it defuses the situation and takes the bite out of their words. You may wish to use it in that situation, and that's okay, it could prove to help even more.
2. Defend your "Attackers"
So someones says a joke. Your manager jumps in and defends you. This is your cue to throw around some of the cliches.
Smile, firstly, and say something like:
Relax, it's just a joke.
We're all just having fun. Don't worry, no harm done.
Honestly, you might want to do this firstly, to get your manager to back off. You can then go back and tell your attackers to knock it off in private, if you need to or if you really want to defend yourself.
^ That's what I would call Divide and Conquer.
3. Help Defend Yourself, but Make Corrections
So your acquaintance says something like:
He didn't mean to take it literally. Lay off him, he can't help it.
Then you can "add" to this:
I can take a joke, it's fine, but maybe it's going a little too far. No reason to fight over it, though.
Warning: this option is very subtle. Your acquaintance may not even realize you contradicted him. Hopefully the others will see it and realize that it's okay to joke around you, respectfully.
If you paint the image that it's okay to joke around you, and your acquaintance doesn't get it, at the very least people will have the idea that they can joke around you, just not your acquaintance. Which really isn't so bad.
4. Talk To Your Acquaintance
Okay so this guy can't take social cues and fails to read situations and simply cannot stop his behavior based on the situation. (At this point it sounds like he is the disabled one).
First things first, thank him. He is trying to help you, after all. He doesn't deserve punishment for that, even verbally.
So start with:
Hey, I think things got escalated a little bit yesterday when those guys were making jokes at me. I really appreciate what you tried to do.
Then lead into what is fundamentally wrong with his approach:
However, I don't think what you did have the intended effect. Those guys are now just afraid to say things around me. I really don't want that.
Then address his goals and ensure him they are being met:
I promise that if they get out of hand, that I can handle it myself. In fact, I will. If I need help, I'll be sure to ask you.
This should almost undoubtedly suggest to him that he stop, without you explicitly telling him to.
I would leave it at that, and if it does happen again, you can re-approach the subject and say something like:
Hey, again I appreciate your effort but now I'm asking you to not defend me. I know you're trying to help, but I am not asking for help right now. I can handle it myself and in the case where I can't, I'll call on you for backup.
You don't have to mean it. I'm sure you don't actually want his help, ever. But opening him up to that possibility will make him feel needed or wanted and pacify him.
For this type of confrontation, you need to use your interpersonal skills to convey to this person that ultimately you're on the same side, but you're just kind of taking charge. If you make him feel like an enemy, he will act like your enemy.
You probably don't want enemies.