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1.
Short for pre-ejaculation, but can be used to replace "bullshit"
"Man, that's a load of prejac!"
"You're Prejacking me!"
by Henry H February 09, 2006
 
2.
An abbreviation to describe a premature ejaculator
Wow, what a disappointment last night was...he was a total prejac, so of course, I didn't get my kicks...
by FlashDanceMOOH September 03, 2009