I hope you do the driving!! You could make him a sign that says "I'm blind I have no idea what she's wearing..." All in good fun there... I used to have a fellow who came in to do work at our office who was blind and he had the weirdest sense of humour - he would tell blind jokes to break the ice figuring it would make people easier around him. Personally it just made me cringe at his sense of humour - he wasn't really funny
. Your friend sounds like a good sport though asking you not to wear it on the drive in!
At my old office building everyone got dressed up one year, but nobody told us in our office (we were renters in a suite there) so I was the only woman in the building who didn't dress up. The next year I wore a costume, and yup you guessed it, nobody dressed up. Thankfully we moved out and now I don't need to worry about that. I work alone, me and my boss.