Why was we don't serve tachyons around here closed? To me is seemed on topic because it asked about the physics in a joke that only physicists would appear to understand.
To be honest, it seems on topic to me. Not the most insightful question, to be sure, but it does take some knowledge of physics to provide a correct answer. I would like to know why dmckee chose to close it in the first place though (foul mood or not, everything gets done for some reason :-P).
I have plenty of physics jokes to share myself, unfortunately, this isn't in the physics SE scope. Your link doesn't work, but don't you have it backwards?
Bartender says "we don't serve tachyons in this bar".
A tachyon walks into a bar.