I've been in those kind of situation. it starts out as jokes, fun and games. everyone laughing and enjoying the moment...stori es are told and then secrets are exposed. interrogation starts, "you did what with who?" and now it's no longer a laughing matter. even though it's history, women are less forgiving, especially if they have been married for a long time and now she's just finding out something new about her husband.
to avoid road trip fights is to limit the amount of partners...2 couples max. having more than that, some can take a joke, some can't, and a few will instigate issues. even though they're all friends, someone's feeling is going to get hurt!