You have to isolate your character from the other characters, so you have him go to the bathroom. Since he's male, he just has to unzip his pants. This helps because seeing another man's penis turns you gay. Why do men in real life pee standing up? Freud would say it's the first conscious expression of a boy's masculinity. A more practical-minded person might simply say it's easier and quicker than dropping trou to sit down. In any case, men tend to pee standing up, both in visual media and literature. Some other things at work here: