I'm a teacher and Head told me this morning that a parent has complained because she saw me last Saturday night in the local cocktail bar having shots.
Apparently it's despicable that an educator of her child would behave in such a way and lead such a terrible example to pupils - as it turns out, her underage DD was with her (must have been at 11pm IIRC) in the adults-only pub and was 'appalled' at Miss Pantaloons' behaviour 

Thankfully my Head is normal and we just laughed our heads off about it. these complaints happen very frequently. A colleague once got a complaint because she was seen with penis paraphernalia in town on her hen do. I think some people think teachers are just robots that turn off at 4pm and have to stay in the classroom over the weekend.
What's the most amusing complaint you've ever got at work?