Maybe two or three times, at a job that dealt with me going to other businesses, I had to use the woman's room either because the men's was out of order or someone was in it taking a prolonged dump. They were all single occupancy restrooms with locks at convenience stores so there was no chance of someone walking in on me, but I still felt hesitant to use them even though the clerks encouraged it when they saw me waiting for the men's room. Only once, when I was finished, did I run into a woman with her kid waiting to use it and I kind of felt strange even though she didn't say anything and it wasn't like we would have been in there at the same time anyway.
The only time I entered a multi-person woman's room where anybody could walk in was accidently at a former job that required foot patrols of various maze-like buildings. I was tired and not really paying attention and when nature suddenly called, I ducked into the nearest bathroom without really looking at the door closely. My first indication that something was not right was the fact before entering the bathroom proper I found myself in an adjoining room with settee-like couches, like a waiting area and remember thinking this was a strange thing to have in a men's restroom. Entering the next area and immediately failing to see any urinals, it slowly dawned on me that maybe I shouldn't be in here and I quickly left without doing my business and confirmed my mistake by the previously unseen sign on the door. I then went to find a men's room, which was only a few feet away.
Luckily this was at 3 or 4ish in the morning and very few employees were around; almost none of them female, so I remember how much worse it could have been if it happened in the daytime and how embarrassed I would have felt with witnesses. After that I vowed to get to learn the property a lot better, particularly the locations of all the bathrooms and look at each door closer before entering

.