Fritz equal 💩 what's the origin of that slang?

Factual Questions
21

My German router is called a Fritzbox. It generally behaves itself and does its job in a reliable manner. Which is more than can be said for various other appliances hereabouts. The word fritz has a positive association.

Dog owners are quite good at inventing euphemisms for the not so cute behaviour of their pets.

22

There’s also Deep Fritz, a series of chess-playing software made by a German company. To my knowledge it’s unrelated to the FRITZ!box brand of wifi routers.