My submissive has a shirt I get her to wear with no bra, that has holes that her pierced nipples will become exposed, when walking through shops or whatever in public. We do this as a form of punishment or just because the attention turns her on.
Only ever attracted one creepy old guy when she was alone... few years back now. Who told her nipple was out and that was disgusting, but he then proceeded to follow her everywhere in the store, still looking at her breast / nipple. (she had to ring me that night)
On the other side, of the scale, had a guy walked up to me and say, don't ever let her go, she is a keeper. There was more to this then just the nipple slip, but her smile lasted for days from this. Other women or guys smile or comment, mostly been positively. Some people blush, and the double take (look) is classic to see.
Not done anything for pissing, in public. Anyway, can I suggest you drink a heap of water, no underwear, white denim or light denim jeans or gym leggings. In public till you have to go, and then you have to keep in public for time after, a food court or shopping centre should maximise your discomfort.
Hope you find these ideas useful.