I have few, if any, deal breakers and fall in with the "if the people I am playing with are fun,cool!" group.
That being said, I will most likely avoid even sitting at a table where the DM's boyfriend/girlfriend/wife/husband/whatever play as well. Last group I played in, the DM's girlfriend magically landed every killing blow on every major monster/boss. Every single time! It was like magic. Those old Chick Tracts were right! Dungeons and Dragons does cause magical effects in the real world!
Seriously. If you DM and your significant other plays in that game, take a long, hard look at how you treat that player in relation to other players.
Does your SO's PC:
- rarely if ever get knocked down?
-always land the killing blow?
-get favorable treatment from opposite gender NPC's regardless of CHA score?
Do YOU the DM feel like if you don't deliver these conditions, you will face repercussions?
If you answered yes to at least one of these questions, you might be annoying the heck out of your other players.