Popped a Red Cap

To masturbate so vigorously that your penis begins to spurt blood

Ricardo popped a red cap while watching Human Centipede.

I just listened to the seminal blues song, 'Red Caps a-Poppin', by Billy B. Goode

Pop a cap of love

When you ejaculate in someone you love

I'm gonna pop a cap of love in you tonight

pop a cap in yo ass

an aggressive term for shooting someone, normally used by those of a darker skin tone or just straight up people from Da Hood.

"drop the money or i'ma pop a cap in yo ass"
"get back here before I pop a cap in yo ass"
"bro, did you hear about the incident that happened the block around the corner? shit was crazy, one dude popped a cap in everybody's ass."