A beer

There's this guy and he goes into the bar and says to the
barman, quick give me a beer before the trouble starts so
the barman gives him a beer.
He then drinks that down quickly and says to the barman quick give me another beer before the trouble starts so the barman gives him another beer.
Same as before he drinks that beer down quickly and says to the barman quick give me another beer before the trouble starts.
Now the barman is starting to wonder when he is going to be paid for the beer so he asks the guy when is he going to get his money for the beers.
The guy says got to go now, the trouble has just started!