Dick slamming describes someone who derives pleasure from repeatedly slamming his penis against an object with a hinge or slide mechanism, such as: toilet seats, bank vaults, cd cases, cars and doors.
When making out with a girl your dick is so hard for so long that when you are done you have left a bruise in the shape of your cock on her inner thigh.
"Hey man, did you guys do it last night?"
"Nah, but we made out for so long that I gave her a dick hickey."
"Pussy."
A friendly competition between you and your friends to see who has the best claim to say, "Mine's bigger." Both more reliable in its results and more fun for the competitors where the results are determined, not by the competitors themselves, but by objective female judges.