I did this in my mid teens at a service station in the middle of a long trip. I'd been holding it for ages and was absolutely desperate when we finally reached a stop. I jumped out of the car, made a beeline for the toilets and rushed into the first available stall. I'd completed my business and was washing my hands, enjoying the feeling of relief when another patron came in and her look of surprise and uncertainty caused me to finally take notice of my surroundings. There was one long bank of stalls and not a single urinal in site. I guess my embarrassed look was enough to relax her because she just laughed and said "I think you're in the wrong toilets!" as she continued into the ladies and I scuttled out bright red and full of apologies.

I'll say this much though, they were some super clean toilets.