sorry

This is a cold joke, which probably means:

Neutrinos travel faster than the speed of light, so when the bartender sees neutrinos (that is, when he walks into a bar), he is actually sitting in front of the bartender. The bartender said, "We don't provide neutrinos." In fact, he is serving neutrinos.

(PS: The so-called smart people are smart. Do you think this joke is funny? )