A bear walks into a bar and orders a beer.
The barman says, "Sorry, but we don't serve beers to bears in this bar."
The bear bangs on the bar. The barman says, "Sorry, but we don't serve beers to bears in this bar, especially not bears who bang on bars."
The bear grabs a passing barmaid and bashes her. The barman says, "Sorry, but we don't serve beer to bears in this bar, especially not bears that bang on bars and bash barmaids."
The bear bellows at the other barman to bring him a beer. The barman says, "Sorry, but we don't serve beer to bears, especially bears that bang on bars, bash barmaids and bellow at barmen."
In exasperation the bear bites the bar. The barman says, "Sorry, but we don't serve bears that are on drugs."
"On drugs?" the bear says. The barman says, "Yes. I saw that bar-bit-u-ate."