Can be used as a noun to refer to a guy who wastes time, is a complete loser, and cannot get anything done. This guy may well be popular with friends, the ladies, and whomever he meets, but has never accomplished anything and never will. Anything he has tried to achieve has ended up in disaster.
That Kramer on Seinfeld sure is funny even if he is a complete jack off.
Steve, did you complete the final report so you can graduate from high school next week?
No. I'm such a complete jack off that I never get anything done.
Smoking pot will really just turn you into a lazy jack off.