When your testicles hurt from ejaculating too much.
Dude, I jerked off so much I think I gave myself mummy nut.
A type of genital piercing in which the foreskin of the penis and bottom lip of the anus are pierced together, connected by a ring. The piercing derives it's name from the sound produced when a person with the piercing farts. The stretched foreskin of the penis causes the sound of the expulsion of gas from the rectum to be amplified. This results in a loud hollow sound resembling a low C note played on a trumpet.
Did that guy's ass just make a low C note? He must have a Jacobs Trumpet.