I've done it before by accident. Especially in clubs or other countries that have cheesy names in place of "Men" and "Women".
Most of the time they just look at you and expect you to turn around but I just head into my stall. Sometimes they call after me and say "This is the ladies room" but I just reply with "I know."
It's not something I do purposely but when it happens I just act normal about it and I haven't been pepper sprayed or tased yet.