There is a little theory that someone once told me, there are two types of people. The people that pee in their wetsuit, and the people that lie about it. So what is it?
I often surf for upwards of 4 hours at a time, and its not really practical to get out of the ocean to relieve myself. Also, as the water can be quite cold, its nice to have my own heating system! Of course, I always rinse the suit (and myself) well afterwards.
I learned 10 years ago to never rent a wetsuit. We were doing the open-water portion of our SCUBA certification in a quarry in PA and the water was ~58. The instructors all sat back in their dry suits and smiled. Our last bit of advice before hitting the water..."if you pee in your wetsuit it'll be much warmer and who cares, it's a rental"