Not tipping on a buy back or a free drink is not just plain wrong it should be against the law and is most definatively a sin. It's assholes that don't tip on buy backs that ruin it for everyone else, cause when a bartender doesn't get tipped on a buy back, they then wonder why bother at all with buy backs or free drinks. Does it not make any sense that if you are supposed to tip on a drink you pay for, you should then show some appreciation for a free one? This is like some sort of alien philosophy to some people. If you just saved the price of a drink ($4 - $8) then tip $2 you would have still tipped $1 why not throw an extra buck to say thanks for saving me money.... you cheap fuck. Don't be a sinner and sacrifice that dollar to the bartender gods, otherwise you will get crappy drinks and slow service and that's a guaranteed.

Now the only exception to the rule is if you get a free drink you didn't ask for. In that case its OK not to tip because he no one ever said they should pay for something they didn't ask for, but then it would still be a nice gesture to leave something :).

DM