I have OCD.

From volume 1 of things not to do in the customs hall at the airport: Have a sudden thought about one's page proofs, and then let OCD take over and find a corner of the room to open up one's laptop so that one can check a formula in the .pdf file while other people are doing the usual thing and going through security. Then spend long enough doing that so that a security guard becomes suspicious and comes over to ask you what you're doing. (I did manage to talk my way out of it, though!) Um, oops?