RPG related quandry ... its an age old one for me as I've had this issue many times in games I've played in and ran and have yet to really find a decent answer other than one I'll provide. But I'm tossing this out in hopes of maybe getting some points of view or ideas I hadn't encountered before.
The problem goes like this:
Player X is your typical happy go lucky ... fun loving ... team playing ... D&D fan. He just is stoked to be at the table, happy to be hanging out with his friends, eagerly anticipating what the DM is going to do this session. This guy is a team player, he wants to get along, ok sure sometimes he will disagree about going right or left, about what to ask a captive, etc. he tends to play "good-ish ... maybe a little neutral at times."
Player Y is not necessarily your typical fun loving guy ... he is a bit edgy (maybe its an act to seem kinda cool ... or maybe he just listens to too much death metal ... and/or watches too much twisted shit on the internet ... probably Japanese or German twisted) ... he generally gets along with people. He knows the rules, has fun most of the time and isn't a jerk at heart really ... he is just a non-conformist. The guy never wants to play anything near a "good" alignment tending character. He hates just going along with the party ... no matter how sound the "group" plan is he tends to want to do something else. He frequently suggests things that are overtly evil ... pulling an NPC into an alleyway and killing them because they have something he needs (when there are non-evil/murderous alternatives readily available) ... etc.
So at the end of the day playing a "good" or "evil" party in my opinion is ok ... either option can be fun ... either option can have good combat or good RP ... or both. I just strongly feel that you generally need to as a group decide this before you start to play. IF you choose the very difficult option of playing a mixed party, and your going to stay true to your character concepts ... you better be ready for some PVP at some point. Again its totally ok if that is what everyone is willing to sign on for ... BUT ... to just randomly pick character concepts and alignments that are in diametric opposition to one an other ... in my opinion ... is just asking for trouble. So my preference is to just play a somewhat synchronized game where the party is loosely on the same page.
This said ... it never fails ... best laid plans soon fall to ruin ... the plans of battle rarely survive contact with the enemy ... the road to hell is paved with good intentions ... yada yada ...
So the question is ... when ... X+Y= Shit^100 ... what should one do?
I mean in the case that player X and player Y are both showing up, know the rules, being polite out of the game ... yet are abjectly miserable half of the time while playing the game ... what should one do? I know honesty is the best policy, but frequently people don't listen or don't understand fully what is being said. So the group talk is had .. and nothing changes. What then? Just quit the game ... reboot without one of them?
This has happened several times to me over the years and it seems like there isn't a good option really.