It's like in the movies, when the bad guy is blackmailing someone, telling him the side where to drop the money, and he's telling to do no wrong moves (no wrong moves = no funny stuff)
Drop the money in the yellow garbage bin in front of the post station. Think about your wife, so "no funny stuff".
if one feels that the comment/remark or passed event strikes them as something humerous one simply states the word "funnystuff". commonly used to replace laughing and normally ends said conversation
Fogey/fogy /fougi/ sl. (early 18C+, orig. Scot) old-fashioned, stuck-in-the mud.
Person with old fashioned ideas which he is unwilling to change: Come to the disco and stop being such an old fogey!
You think me an old fogeyand an old tory, his thoughtful voice said. I saw three generations since O’Connel’s time. I remember the famine. Do you know that the orange lodges agitated for repeal of the union twenty years before O’Connel did or before the prelates of your communion denounced him as a demagogue? You fenians forget some things. (James Joyce, Ulysses. PenguinBooks,1992. p. 38)