“What is the number for 311?” you ask, barely suppressing your giggles, and thus alerting your interlocutor to the fact that you have a zowie of a punch line stored up.

“Gee, I don’t know,” says your interlocutor, playing along with a strained smile. “What is the number for 311?”

“412-255-2621!” you reply, and fall rolling on the ground, unable to control your paroxysms of mirth.

This notice is printed on the lid of every city-issued recycling bin.