What secret should my character have?

I’m writing a script, and to make it (more) interesting there’s this person in the background action that has to have this really weird secret or fact about themselves. Unfortunately I’m not sure what this is, so I’m in desperate need of some ideas.

This could be like a brainstorming session. I’m not asking anyone to write an intricately detailed plotline for me, just throw some weird ideas out there. Please. Thank you :)