I've used gents - deliberately when the queues at the ladies were stupidly long and the gents were dashing in and then getting straight out again - it was at a concert at Wembly, and I didn't see why I should spend the interval hanging round in a queue when there was a perfectly useable loo in the next door set of toilets.
Now and again with less deliberate choice, and only realising when coming out. On those occasions, I didn't spot the stinky trough, and as it was in France, the smell/state wasn't much of a clue anyway.