Before Trouble Starts

A guy goes into a bar and says, Quick, a pint of beer before the trouble starts.
The barman looks around the sleepy bar, shrugs and pours a pint for the guy.

The guy drinks it fast. Quick! another pint of beer before the trouble starts.

The barman looks at the guy oddly but pours another pint and gives it to him.

The guy drinks it fast. Quick another pint of beer before the trouble starts.

Barman pours a third pint with a frown on his face but hands it over reluctantly.

Again, the guy drinks it fast. Quick another pint of beer before the trouble starts."

The barman replies, Look what trouble is this then?

I haven't got any money.