Give him a beer

A cowboy in a bar asks the waiter:

“Give me an beer !”

“Not to say  an beer  but  a beer !”, says the waiter.

The next day the cowboy comes back to the bar and says:

“Give me an beer !”

“Sir, it’s not an beer, it’s a beer ! The next time you come ask correctly: A BEER.”

The third day the cowboy comes again:

“Give me beer !”
The waiter is surprised and asks:

“How many ?”

“A !”, the cowboy replies.