YTA. You and your friends could have taken the energy y'all put forth in the "clever" thing y'all did in the theater into telling him to stop talking with food in his mouth. Show him the bits and pieces of food right then and there; he wouldn't be able to deny it and he'll also see what he's doing. If he continues, then tell him you can't do this anymore and leave. You could have also taken the energy you used to post this online to tell Oliver you're sorry for how you went about things, but you have something that he needs to know. Again, if he doesn't change, then stop hanging out with him. You're not asking him to change his personality, just improve his manners. That's what a true friend would do. You seem irritated, but you are a bad friend looking for the support of complete strangers to treat someone badly instead of growing a pair (of balls or of ovaries) and helping your friend become aware of how gross they are presenting themselves when the talk with food in their mouths.

YTA for not being honest and learning to say: No. I get it, you don't like Oliver. And that's fine. But then don't give in to 'keep the peace'. That's just disgusting. Stand up, be an adult and say: No. Hey, my internet is down, you should buy my ticket. No, I won't. It's that simple. You don't have to argue. Whatever he throws at you, all you have to say is: "no, I will not." Or: "No, I don't have to do that." And as hard as it is, if he asks why, tell him the truth: I won't buy your ticket because A: you never pay it back and B: you're a liar. If you had no internet, you couldn't even write me. Also C: I do not want you to come with us because you spit on my snacks and ate annoying. But you string him along and enable him, and that's why YTA. You deserve all the misery he brings you, because you xou don't tell him to stop and don't say no although you could. No one forces you to go along. He's not a rapist with a knife or another kind of offender who has power over you. You're just a doormat who can't say no.

It's nice that you are now making your own articles, BP, but this formatting is awful to read

The "protagonist" of this story should have just told Oliver, directly and sincerely, that his behavior was bothering them, instead of lying and then covertly sneaking away (which sounds like a very childish thing to do). So this is a definitive "YTA."

You’re a bad person and absolutely YTA. I have a hard time believing you’re over 14 years old. Pretending to be someone’s friend then talking behind their back, doing childish things like ditching them, and not being forthright about your complaints To the person is far worse than just telling him you don’t want to be his friend. Also, if you don’t want him coming, why are you inviting other friends where he can overhear? That sounds deliberate and extra cruel. Go look in the mirror and tell yourself to do better.

And reason you couldn't just grow a pair and ask him to stfu/stop spitting on you? Your reaction was childish AF.

YTA and a terrible friend. If you are friends like you said, just talk to him (one on one, not in a group). If he doesn't put in an effort to not spray chewed up food at you then I suggest re-evaluating your friendship.