Deal breakers for me depend on who the person is, but, generally, as my friendship has been deteriorating with my friend from high school for the past month or two, I can think of a few things that are deal breakers for any friendship of mine based off of my experience with him:
-Getting upset over what game system I play on: considering that the XBone is going to have cross-platform compatibility with the PC to some extent, I do not know why my friend wants me to go and buy a system that I have told him on several occasions that I do not want. I realize it may be a feature not supported by every game that comes out on the system, but the way he acts towards me about the issue has led to arguments in the past between us that has made me wonder why we are still friends. I mean, we both like to play video games, even if we have different genres of interest, and it's not like I am acting like playing on consoles is a bad thing. It's just that, for the first time in my life, I feel like building a PC so I can play everything without having to worry about whether the PS5 or the Xbox Two (or whatever the next potential system will be called) will be able to play everything that I spent my money on in the past. If I want to play Bioshock Infinite or Far Cry 3 20 years from now, as long as DirectX and all the other software still supports the code to play games from that era, I'll still be able to play the game and feel like I got my money's worth.
-People who act like they know what they are talking about when they have not done their research, and won't admit to being misinformed: for those who have kept up with the COD series, you would know that the games are being made by three different companies right now: Infinity Ward, (who, from what I've heard about their games post-MW2, are a shadow of their former selves) Treyarch, (my favorite COD dev atm) and Sledgehammer Games, who made COD: AW. My friend does not like Sledgehammer Games because they "ruined Zombies in COD" by making the Zombies mode in Advanced Warfare supposedly worse than Treyarch's. To each his own, (I haven't even played the game myself) but that is not what gets me mad: he acts like Treyarch, whose pockets are being filled by the same publisher as Sledgehammer, is going to sue Sledgehammer because they stole the idea of COD: Zombies from them, like Treyarch owns the IP to COD and all of the modes produced therein. I try to tell him how his logic makes no sense, but he gets mad at me because I supposedly never let him win an argument, which is so far from the truth that it's not even funny. If Treyarch was going to sue Sledgehammer, there surely would have been some news about it on the Internet, of which the only COD-related suit that I found in my research was between Infinity Ward pre-MW3 and Activision. I don't mind someone not being informed about something they don't really care about, but when someone is just defending their own ego because it's being done by their favorite company, I can't help but feel like I am with someone who is worshiping the Golden Calf metaphorically speaking. The thing is, too, I am trying to be his friend by pointing out flaws in his thinking so he can try to think rationally about things and carry on an informed conversation with others, but it's like he wants to stay in the dark about how that works. Which is his decision, so there's not much I can do about that.
-People who try to take things more seriously than they really are: I was playing Smash 4 on Wii U once with my friend, and I happened to win the fight. For the record, I tended to win a lot of the fights that I played with him and his friends and siblings. Anyways, I won and I made a comment to the effect of "Got you!" in a playful manner. My friend's reaction? He goes up the stairs and says I owe him an apology for "making fun of him." I was thinking, "You can't be seriously mad after losing only one match." I apologized to him, but he still takes other things more personally than he should. Sometimes, when we are playing Zombies, he will just get upset after going down several times to the point of just ragequitting the game, even if doing so will ruin others' fun at the moment by ending the game. I try to convince him that it's just a game, but he acts like little things just tick him off and that he claims that he "doesn't know" why they do that.
Stuff like this has made me consider breaking off my friendship with him, considering that, while I may get frustrated at a game at times, I usually can contain my frustration enough to not just completely quit and ruin other peoples' fun. Granted, he has his own problems when it comes to controlling his behavior (nothing violent, thankfully), but I can only tolerate so much as I get further into college and other things come up in life. The only reason I have not broke off my friendship with him is that he's the only friend I have in real life right now. I still have yet to check that video game group at college, so hopefully things will change for the better soon.
Once again, I typed up a wall of text. I really should become better at saying what I want to say in forums in a smaller and more concise manner...