Two dog owners are walking their dogs down the street...

... they pass a bar, and the owner of the German Shepherd suggests they pop in for a beer. But the owner of the Chihuahua hesitates.
"I don't think they'll let us in there with our dogs," says the Chihuahua owner.
"Sure they will, watch this," and the German Shepherd owner pulls out his sunglasses, puts them on, and walks into the bar doing his best to act like a blind man.
Through the front window, the Chihuahua owner plainly sees that the bartender has assumed the German Shepherd is a seeing eye dog. He even buys its owner a beer.
"Might as well give it a shot," concludes the Chihuahua owner who, putting on his sunglasses, enters the bar.
"I'm sorry, sir, we don't allow dogs in this bar," says the bartender.
"No, no, this dog should be okay," replies the Chihuahua owner, "this is my seeing eye dog."
Dubious, the bartender asks, "a Chihuahua? As a seeing eye dog?"
"... they gave me a ***Chihuahua***!?!?"