A Wank-Shake is a filthy prank played by mcdonald's employees on innocent customers, who purchase any variety of milkshake, from a drive thru. to do this male employees will wack off into your milkshake thus creating a Wank-Shake. The symptoms of obtaining a Wank-Shake are: extra saltyness, your straw becoming blocked due to chilled spunk, stickyness after drinking milkshake and most of all, circular swirls of cream/white in your milkshake, due to a cheap attempt to cover it up.
Customer: "excuse me sir, i didn't want vanilla swirl in my milkshake!!"
Employee: "noo mate thats no vanilla!!!, (sniggers to others).
Larry: "did you sort that posh twat in the mercedes a Wank-Shake".
Barry: "ov'coarse mate, a nice steamy one, Wank my cock!! haha!!!!"..
Larry: "Lerious-character!!! hahaha!!".