Deal-breakers... I'd say I'd show up at a table expecting to use the rules to resolve situations. There are things that would turn me off from a game pre-emptively, like most homebrewed worlds that aren't very fleshed out, or excessive house-rules (especially house-rules that look like they were written someone who played older editions/systems and wanted 5E to be more like that).
But the deal-breaker during play I think would be not using the rules, and this comes in two flavors. One, excessive "roleplaying", or improvisational theater, on the part of players and DMs, that has nothing to do with advancing the game (I've only seen this occasionally, but damn is it annoying). I don't mind some world-building or character development (and don't take this statement the wrong way, I love an immersive world and being engaged in a fantasy setting, and I love thinking about how my character would react to situations rather than thinking about the best mechanical benefit to a given scenario), but keep it focused. I have to think that DnD is not the optimal system for a kind of game that doesn't focus on dungeon crawls and/or adventuring days. As for the second flavor, that'd be those who don't know the rules and basically make up stuff as they go. Like, dude, consult the PHB and see if there's a rule that covers that situation first. It's all right to improvise sometimes, and there are a lot of things the rules don't cover, but some of us built our characters under the assumption that the rules would be followed as they're outlined in the rulebook, and you run the risk of making us think our choices don't matter when you can't be bothered to follow or know those rules. Those kinds of things would turn me off of a table and eventually result in withdrawal from the game.