I am too stunned to say anything to him...(should have said something like "enjoy the show?!"), so I don't. I am too disgusted to try on anything else, and leave the fitting room. I ask to speak to a manager, and I explain to her what just happened. This scuz ball of a dressing room attendant has just seen me pretty much naked, was peeking in on me...and what does she say? "I'm SURE he wasn't trying to do it intentionally! I'll talk to him about it". ARE YOU FUCKING KIDDING ME?
I'll be calling corporate tomorrow.
EDIT: I called corporate, and told a customer service representative. She was shocked, and horrified at what happened, which really makes me justify my anger. She thanked me for telling her, and she filled out a report that she will be submitting to the district manager, the store manager, and I think she's opening up a country-wide investigation.
Thank you all for your advice, and help!