Before the trouble starts

[NETim]

A man runs into a bar and yells, "Quick, gimme a shot of whiskey before the trouble starts!"

The barkeep obliges.  

Another man runs in and shouts the same thing.  The barkeep obliges.

Soon a third man runs into the bar and shouts, "Quick, gimme a shot of whiskey before the trouble starts!"  

The barkeep pours him a whiskey.

"Now, who's going to pay for these drinks?" asks the bartender.

"OH OH! Looks like the trouble just started!"