I put this as a comment on my peeing at parties post, but thought it deserved it's own post so I'm putting it here.
A while ago I made a few polls on MisterPoll about this and got some great results. Here they are.
Girls Naughty Peeing:
Here is the CSV from it (has a lot more information in it)
Girls Naughty Peeing at a Party:
Girls peeing inside at house parties