The Drinks Are On Me

This guy staggers into a bar and shouts, "A double whisky please barman, and a drink for everyone here... and while you're at it, have one yourself."
"Well thank you sir," says the barman and proceeds to pour everyone their drinks.
Moments later the guy shouts, "Another whisky for me, and the same again for everyone else."
The bartender looks a little worried now and says, "Excuse me sir, but don't you think you should pay me for that last round first?"
The guy slurs, "I can't. I don't have any money." With this the bartender flies into a rage and literally throws the guy out of the bar.
About twenty minutes later though the guy staggers back in and shouts out, "A double whisky for me, and a drink for all my friends."
"I suppose you'll be offering me a drink too?" the barman asks, marvelling at the guy's nerve.
"Not likely," slurs the guy, "you get nasty when you've had a drink!"