Hahahardon
When a situation is so ridiculous it makes you laugh and also makes your penis decide it wants to be involved.
The guy at the bus stop was yelling at a pigeon like it owed him money. I laughed so hard my penis stood up.
My teacher told a joke about a math problem that was actually a love story. I laughed so hard I got a boner.
I saw my dog trying to eat a sock and it looked like he was screaming. I laughed so hard I got a hard-on.