machine gun masturbation 

To masturbate even after you've ejaculated.

Derek couldn't stop masturbating, thus commiting machine gun masturbation.

machine gun masturbation by B ryan October 6, 2006

Machine Gun Masturbation 

When a man masturbates and when it seems he is finished he keeps going, thus making it hurt, this is machine gun masturbation.

Johnny was so horny he said he was going to use machine gun masturbation on his girlfriends face while she was sleeping.

Machine Gun Masturbation by Lol'd on your mom October 5, 2006