"Trouble at the local bar..." joke

A guy goes into a bar and says, "Quick, gimme a beer before the trouble starts!" The barman looks around the sleepy bar, shrugs and hands the guy a bottle of beer.

The guy drinks it fast. "Quick! gimme another beer before the trouble starts!"
The barman looks at the guy oddly but hands another beer to the guy.

The guy drinks it fast. "Quick another beer before the trouble starts!"
The barman hands him another beer, with a frown on his face, but hands it over reluctantly.

Again, the guy drinks it fast. "Quick another beer before the trouble starts!"
The barman replies, "Look pal, exactly what trouble are you talking about?"

"I haven't got any money!"