An infectious organism walks into a bar. The bartender exclaims, "We don't serve infectious organisms in here." The organism complains, "Well, you're not a very good host."

Two bacteria walk into a bar. The bartender tells them, "We don't serve bacteria in here." The bacteria reply, "But we work here! We're staph!"

An infrared photon walks into a bar and asks, "Is it hot in here, or is it just me?"

A neutrino walks into a bar and says, "Don't mind me, I'm just passing through..."

A room-temperature superconductor walks into a bar. The bartender says, "We don't serve any superconductors in here." So the superconductor leaves, without putting up any resistance.

Schrödinger's cat walks into a bar-and doesn't.