pretty self explanatory. An act of jerkin it, or tuggin the bugger. Otherwise known as masturbation
Jon: "Yo, did you do your english assignment last night?"
Me: Nah man, I was preocupied jackin the beanstalk.
Jon: You been jackin the beanstalk AGAIN?!
Me: 3 times a day bro.
12 Oktyabr 2007