We're not going to ask for credit card information for just those reasons, Zanzibar.
Generally - it's even harder to deal with someone who says only an inappropriate line or two as opposed to a whole load of it. A GM can't be around to catch 2-3 lines by the time they are said, and if confronted, the guilty party can always make (sometimes surprisingly) convincing denials. We can keep track of how many times people complain about someone, but that is way too easy to abuse and definitely not a good way of deciding on appropriate GM action.
How do other games deal with such things? I've never really researched that.