We're starting off with a big one, because this is something so different about guys and girls, it has to be chromosomal. Not only do guys not want to talk to each other while using the bathroom, they will go to great distances to not be stuck in that middle urinal when the two on the outside are occupied. (Sorry, sink. You might be taking one for the team)

Girls, on the other hand, will duck into the bathroom for a myriad of reasons that have nothing to do with relieving oneself. Anything from idle gossip to reapplying makeup to just needing an excuse to get away from an awkward or boring conversation can send a pair, trio, or even quad of women hightailing it for the john. And that's totally fine, it's just not something guys are ever going to do.

But just so this seems balanced, ladies, did you know that guys almost always spit into the urinal as they're doing their business? It's an almost uncontrollable impulse that researchers at Boise State (via New York Magazine) attribute to being territorial. That has to be just as perplexing to women as the bathroom being used as a social recess is to men.