In my experience, most of the time, you'll be totally safe if you just go in, do "your business", wash your hands, and leave. I've done this A LOT of times, and as long as you're halfway passing, you'll be ok. Don't speak to anyone else, don't try to fix your makeup or your wig (unless you're by yourself in there), just get in and get out ASAP.
That's just IMHO. YMMV.
Carol