A man and a bartender

A man walks into a bar, sits down and orders .

He says "Give me a beer before
problems start!"

The bartender doesn't understand but gives the man a beer....
After 15 minutes the man orders a beer again saying "Give me a beer before problemsstart!"

The bartender looks a little bit confused but gives the man a beer.
This goes on the whole night and after the 15th beer......

the bartender is totally confused........and asks the man 

"What do you mean with before problems start? And when are you going to pay for all the beers you drunk."
The man answers "You see, now the problems start!" hahha.....