There is no good outcome if you hit "Reply All" when you meant to reply to just one person. There are just varying degrees of humiliating consequences, from suffering the indignity of your coworkers simply thinking you suck at email all the way to getting fired for accidentally telling the entire company your boss had chode fingers.
Last week we discussed our most memorable chat window screw ups, but it's even easier to accidentally group reply to emails. The Reply All button's prominent placement is a scourge. It is the killer of surprise party planning and secret crushes, the destroyer of reputations for not trash-talking colleagues. And we want to know the worst things that have happened when you accidentally pressed it.