This is the key, and the most valuable comment in this entire thread. Just like making moves on people, the smartest tactic is to go as far as you feel like going, carefully, until it's not symmetrical.

The women I work with in IT have had incredibly adult jokes made about them and vice-versa, because it's known and comfortable. If it wasn't mutual, you should know to back off, because they aren't going to lighten up.