Nice one. The first two lines are pretty funny on their own, with "got a match?" as the punch line. Actually, just the thought of a hash slice and a regexp sitting in a bar together makes me chuckle.

Here's my attempt at making a different joke out of your punch line:

A substitution, s/\//\\/, walks into $bar and sits down and orders a beer. Already sitting next to him is another substitution, s/^$//e, holding a scotch and soda in one hand and staring expressionlessly at the pack of cigarettes she's holding in the other hand (camels, of course). s/\//\\/, hoping to bum one from her, asks her whether she wants to have a smoke together. She replies, "I'd love to, but I haven't been able to find a match."