There's a big conference of beer producers. At the end of the day, all of the presidents of all the beer companies decide to have a drink in a bar.
The president of 'Budweiser' orders a Bud, the president of 'Miller' orders a Miller Lite, Adolph Coors orders a Coors, and the list goes on.
Then the waitress asks Arthur Guinness what he wants to drink, and much to everybody's amazement, Mr. Guinness orders a Coke!
"Why don't you order a Guinness?" his colleagues ask.
"Naah. If you guys won't drink beer, than neither will I."