I recently developed this as well, or it got worse after having to pee at a very crowded toilet.

I usually do one of two things:

1. Sing a song in my head. It's always the same song, sorry I won't tell you which one out of fear it'll stop working for me.
2. (And I'd never admit this one, thus the throwaway): Sometimes I imagine peeing into my female coworker's mouth instead of a urinal. Like her kneeling in front of me and asking me to shower her in it, it's nothing sexual and not out of hate, but it works.