When you’re comparing sizes
When they accidentally walk in on you changing, into either different clothes or a monstrous werewolf at the full moon
When penis jousting
When you’ve given up on the world and clothes are too much effort
When you’re oiling each other up for gladiatorial combat (How else are you supposed to get oil on those hard-to-reach places?)
When you’re having sex with each other

-S. Savitz