I'm surprised nobody else has run into this problem. I guess I look like a criminal

Probably more likely that I change in stores often since I am on the road a lot as a consultant.
While it sounds nice to throw a stink and shove ADA rules and threats of lawsuits in their face, I have to think about the reality of the situation. The last thing I want is police showing up to make an official statement or having to testify about my situation. I know I would win in the end and probably end up with some dough but their is no way I can make myself go through the embarassment. Hard enough to talk about it with friends and family. I have seen the reaction of the few employees who made sure I was not taking store products in; a facial expression of trying to hide the fact that they were giggling on the inside after seeing the brief. I think trying to hide the bringing in of the briefs would make it worse since that is exactly what real shoplifters do. At least 95% of employees have a brain big enough to know that no real shoplifter would openly carry in a product they intend to steal.