My 2 favorites...

Waiting at the departure airport for the weather to go above mins at the destination due to fog. Passenger in 3B tells us we need to go because he just called his friend and he can see the stars.

Show up at the podium on reserve call-out. Introduce myself to the Captain I'll be flying with.
CA: "You are a jumpseater?"
Me: "No, I'm your FO"
CA: "Where did my FO go?"
Me: "I don't know."
CA: "When did they call you?"
Me: "Four hours ago."
CA: "But we were still flying in from XXX, the FO didn't say anything about being sick...(long pause)"
Me: "Wow, those are shiny shoes, you do that yourself?"