Masturbating for hours on end while high and/or getting on meth, generally only cumming once at the end.
Hiding from the world, not answering phone calls, watching endless porn sometimes on fast forward, very brief feelings of filth and disgust immediately upon completion.
These are all tell-tale characteristics of a Jack Mission. Pornographic material of some kind is almost always present.
Sometimes abbreviated phonetically as... Jack Mish
"Sorry for lagging, got some new porno movies... been on a Jack Mission."