An infectious disease walks into a bar.
The bartender says "I'm sorry, but we do not serve infectious diseases."
The disease says "Well you're not a very good host."
Two bacteria walk into a bar.
"We do not serve bacteria here."
"But we work here, we're staph."
An IR photon walks into a bar and says "Is it hot in here, or is it just me?"
Schrödinger's cat walks into a bar.
And doesn't.
Also, all credit to Brian Malow.