There's as many bar rules as there are bars:
* Open off break/take what drops
* Call kisses (usually yes)
* Call side rails on 1-rail bank shots
* Call side rails on 1-rail bank shots except when it hits inside the last diamond
* Base of ball vs. all of the ball out of the kitchen
* 8-ball has to go clean/doesn't have to go clean
* Scratch on break=loss
* 8-on-Break = win; 8-on-Break = loss
* Failure to contact 8-ball = loss (Usually, you just have to touch the 8-ball, not get a rail.)
* Spot a ball following a scratch if they're all in the kitchen
* Can't use any of the other guy's balls in a combo, even if you hit your own first.
* 8-ball is neutral (can be hit first in a combo)
* No safeties
* Last pocket vs. straight in (e.g., when you get down to the 8 and call it, they say, "hey, we always play last pocket here." This usually happens right after you shoot your last ball in a side pocket.)
And probably a bunch more I'm not remembering at the moment. What do you do when someone comes up with a crazy rule? Well, I'm just a B player, but that makes me a pretty heavy favorite in a bar like the one you describe (that is, not a pool hall). And if I'm not the favorite I can usually figure it out pretty quickly.
So when I'm not in my home bar and one of those rules come up, I just say, "Oh, that's how you play it here. Fair enough" and play accordingly. I'm the favorite either way, and it keeps things friendly while letting me lose a few games along the way, which also helps keep things friendly.
The two things I always ask before a game are (1) Is the table open off the break? and (2) Does the 8-ball have to go clean. The rest are pretty minor and you can deal with them as they come up.
Cory