Here's a trick for finding out if something is sexist, which can also help you understand why it's sexist. Replace "women" (and "female" etc.) with "black people" and see if it suddenly sounds incredibly racist.

Haha, having black people serve beer would be incredibly racist.

Alright, fine.

If you enjoy women, why not let them do something other than get the beer?

I think you're assuming something I haven't said.