Jenking off is the act of taking a big whiff of jenkum before jacking off, using the left over sewage from the jenkum bottle as lubricant.
I heard Steve jenking off in the bathroom at school.
What Chicago White Sox fans do when Bobby Jenks comes into the game in the 9th Inning to close it out
"Dude we're up 6 to 5 going into the top of the ninth. I can't believe how hard I'm Jenking Off right now".