This isn't exactly a knee slapper but I found it somewhat humorous. On a transcon flight not too long ago, the line to the FC lav stretched down the aisle into coach. It seemed there were always a half dozen or more folks in line.
We were at cruise altitude, flight was smooth, not a cloud in sight. The pilot announces that he has a report of turbulence ahead and would all the pax immediately return to their seats. Once everybody was buckled in, the cockpit door opens and the pilot heads to the lav at a fast trot. He was in there for a looooong time!
Once he vacated, the co-pilot hits the lav. Once they had both done their duty, the cockpit door closes, the seatbelt sign is turned off and the line to the lav forms again.
Never did experience the slightest turbulence! Guess it's better to be safe than sorry....