I think we've all been in that situation of when you've got to go, you've just got to go. I like to ask FA's to use a little discretion when letting someone use the lav while taxiing. Simply call the flight deck and we will stop, or we will wait to move again. I'd rather that, then have a big mess to clean up in the end. Most FA's are really good and will use their best judgement, but I've known of a handful that wouldn't think twice about calling us up and saying we need to have someone arrested because they got up to use the lav. Really puts us in a bad spot then. We want to back up our crewmembers but we also owe it to our customers not to have someone be kicked off for something they really couldn't help.