The Strangerfish is what is known in the masturbatory world as a combo-jack (You earn bonus points for technicality with these sort of moves).
You will first need to start out with the Stranger. This involves sitting on your hand until it goes numb. The loss of the feeling in your jacking hand creates the illusion that a stranger is in fact jerking you off.
Once you have lost the feeling in your hand and are in stranger mode, you will then need to make a quick switch to the Stalefish (It is crucial to make this transition quickly before your leading hand regains feeling). The stalefish involves standing up, passing your jacking hand under your leg and proceeding to jerk off in this challenging position. This was named after the classic skateboarding trick which involves a similar motion.
If at this point you have pulled the full move off successfully without harming yourself or others, go get yourself a Klondike Bar. After all, you deserve it for your Jedi-like wanking skills.