A situation similiar to blueballs in which a man is on the very tip of ejaculating when his ho totally ditches him or does something to stop him from shooting his wad, jamming his cock with semen in the process. Also can make urinating quite difficult afterwards.
AKA the very worse weapon the cocktease has in it's arsenal. The ultimate bait and switch.
Dave: "Man, I was totally getting a handjob from Jenny but that bitch totally cockjammed me by saying she had work in the morning and telling me to rub one out on my own."
Phil: "That sucks bro. What a fucking Cockjammer. Well at least you almost busted a nut."
Dave: "Bust a nut?!?! She almost busted MY FUCKING DICK!! It hurts when I touch it. I think my penis knew she abandoned it before the deed was done. It's extremely angry about the whole ordeal. Oh, and the best thing was I couldn't piss for 4 hours either."
Usually a penis that can drive into people or objects with as much force as a hammer. It can be used in multiple ways like the word fuck, and is more cool when you type it in all caps.