I was having lunch in the old-fashioned cafe Heinemann. Before lunch I had to use the men's room. Since the pissoir was occupied I used the "normal" toilet. While I was washing my hand the lavatory attendant approached me. (Heinemann is of the rare cafes where you still have a lavatory attendant.)
"Mister," the lavatory attendant said, "would you be so kind to follow me?"
I followed him. We went into the toilet. He pointed at a few drops of liquid on the floor.
"This is your piss," he said, "Why didn't you use the pissoir? Now I have to clean up after you."
"Well," I said, "The pissoir was occupied. And this is not my piss, it's somebody else's piss."
The lavatory attendant shook his head. "This is your piss," he said. "I'm cleaning this toilet every tien minutes, and this is your piss, mister. I know what I'm talking about."
I almost got upset but then I decided that this was Dada in its purest form. German Dada maybe, but German Dada is also Dada.