Personally I never had a problem going down on my ex even during her "time of the month." You just have to be more careful about it. So you can't stick your tongue in her hole or up and down her slit. But you can still lick around down there and drive her crazy, and then just go straight to work on the clit. Cause unless she's using pads or is very unsanitary, the clit's not going to have blood on it anyway. But maybe that's just me, cause whenever my roomate's gf is having her period, he says she just gave him head and he didn't do anything. And I sit there calling him a pussy cause he wouldn't just go crazy on her clit. But maybe I'm just crazy.