What do you do when someone locks their bike to your property

What's annoying about it?

Or if you're feeling spiteful put loads of crumbs on it so pigeons shit all over it. That'll stop em putting it there again and its not like you'll be blamed-he'll just think there's an epidemic of diarrhitic birds on your street. Or you could shit on it, but thats less subtle, and your neighbours might object.

Put an extra lock on it and a note.
Then when he contacts you to get his bike, you can smash his face with a golf club or just give him a verbal beating. Whatever you prefer.

The bitter shithead in my says steal the bike or put another lock on it, but that would be a such a dick thing to do.

this this and this, in any order.