When a group of kids sit around and do nothing but chill and sometimes hit the bong
Jake: Dude what are you doing right now?
Patrick: dude I'm just jerkin it
Jake: you are what?!? Dude that's gross
Patrick: nah dog I just sitting here doing nothing you freak
Person 1: Hey have you done the calculus homework yet?
Person 2: Not yet, I am currently jerkin' it though.
Person 1: Dude wtf, I don't need to know that
Person 2: Huh, its problem 3. We must solve for the third time derivative of thr given position function.