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Is when a guy ejaculates before even inserting himself into the chick.
Damnit bill you prejaculated on my leg...sorry monica.
by Smalls08 January 01, 2008
Premature ejaculation:

Usually used in reference to a situation in which someone is beating it up and accidentally skeets inside of someone they didn't plan to.
"I was beatin' it up raw last night and I accidentally prejaculated in that hoe before I could pull out. I hope she don't get pregnant."
by Nullpersona January 06, 2008