I think the classic example of this is the guy who wants to be evil in the middle of a group of good guys, but somehow expects no party issues.
Again, city creation is your friend. If you have one white council wizard, one apprentice wizard, one minor talent PI, and one guy who wants to be a magical ninja assassin clown tree, then you have to sit down at character creation and get a story going as to why the other 3 would ever choose to call this guy up and invite him on an adventure. A story that has to make sense and be cool to FIVE people.
It's a pretty great equalizer, and I wish I had done it more with my group, who somehow went with 2 holy roller angel types and 5 other people lawbreaking... a lot... (and this was with mutual character creation).