Rule of Comedy: Know Thy Audience
The other day I was over at a friend's place watching Season 1 of Battlestar Galatica (the remake, not the original series). He doesn't care about 24 so I'll have to catch up on that later. Anyhow, it was the season finale of season 1 where the crew is wandering through space and they discover the planet Kobol.
I turned to my friend and said "Whew, it's a good thing they didn't land on the planet Fortran!"
He looked at me, not getting the reference. "Fortran?" he said. "What's Fortran?"
"Uh, never mind," I said. "The joke wasn't very funny anyhow."