I think most intoxicated men are unlikely to be outraged, I suppose a parent might be if they took a child in and saw you; but night times in pubs are not usual spots for kids.
I certainly think the outcry would be less than a man in the ladies toilets peeing.
Only once have I come across a lady in the gents, that was at Tower Bridge in London; where a lady had decided she didn't want to queue for the ladies and gone into the gents leaving a young boy on lookout, however he never said anything as she flushed and made her way out of the cubicle. I admit I had second guessed the situation. The Urinals faced away from the cubicles so I had my back to her, but a full length mirror on the opposite side above the sinks showed me side on and I made damn sure my cock wasn't shielding by my hand. She caught a glimpse in the mirror and hurried out of the toilet whilst telling off the young boy.