Step 2: Being appropriate.
Try not to make a joke about their anatomy, in fact just don't, you shouldn't have to try not to.
Don't ask invasive and annoying questions just because they happen to be a female, the internet is a vast place, some of the information you seek is out there, some things are best left unasked.
You can however engage them in normal conversation and they will respond in normal ways, you could make a joke about how few girls there are about the internet, as long as you phrase it sensibly, examples being:
- Man this place was a sausage-fest before you showed up
- Wow, chick on the internet, bet you're lost (this one is a double whammy of idiocy, see there's a bit of chauvinism in there too, best left unused)
- Are you really a middle aged man?
Really it's not the best of jokes anyway but made appropriately or as an actual comment I suppose it's not that bad, but again it's probably very repetitive at the end of the day.