The attitude was totally unacceptable. If he really had to go, he could have explained and stepped into a stall (assuming they were unoccupied as the cleaner had "closed" the RR).

As to what to do? If I'm the only person around, hope the attendant steps outside while the man finishes his business and sympathize with her about the "jerk". Not quite sure what you mean by "the only person around", but assuming there are employees in the lounge, I would definitely report him. I also like the idea upthread of advising the airline/GA that he is likely intoxicated & maybe should be denied boarding.