Really? Crap, that's awful. DCA is unique due to its' nearness to the Capitol, but that still doesn't give the TSA there the right to treat you that way, especially over such a silly issue. Whenever I went through security at DCA, it was pretty normal like any other airport (but a bit more stricter), so I'm guessing this was specific to that one TSO power-tripping.

If I were you, I would have complied, taken off my sandal, went through security, and when done, go to another TSA officer and ask for a comment card and/or manager's phone number. If that still didn't work, I would have boarded my plane, then when I get home, call the TSA 1-800 number. Additionally, I would gather that guy's badge name.

IF you had a lot of time to kill, you could have miscooperated, and a LEO would come. Then, explain the situation to the LEO and tell him how you're being treated. At least a LEO is trained to be courteous in situations, dislike TSA, from what I see. Or, leave security right away and go to your airline's check-in counter and explain the situation, and have the person come and help make sure you're treated correctly - because the more witnesses, the less TSO will be likely to pick on you.

Next time, perhaps.