I tried to use the bathroom as I was leaving, a guy who hadn't been around (hiding in the back maybe?) was standing by the door and demanded 1000ru to use the bathroom, I refused and went to leave. As I got out the door the bartender was at the bottom of the stairs mocking me, I turned around and gave her the finger (I know I know..). She shouted to the bouncer who ran after me and physically dragged me back down the stairs by the leg, claiming that I now owed them 'disrespect' money to the tune of 12,000ru.

They locked the door and wouldn't let me leave for about an hour as they tried various ways to get money from me.

The other guy that replied to you claims it could be for an unpaid tab, but I've never been to a club in Russia that does tabs, you have to pay for each round as you order them.