The bartender says, "Hey buddy, can't you read that sign? It says no dogs allowed! Get that mutt out of here!"
The man replies, "No, I can't read the sign - I'm blind, and this is my seeing eye dog." The bartender is embarrassed and gives the man a beer on the house. Later that day, the guy is tells his friend how he got a free beer.
The friend thinks a free beer sounds pretty good so he takes his dog into the bar and sits down. The bartender says, "Can't you read the sign, buddy? No dogs allowed! You'll have to leave!"
The friend says, "Sorry, I can't see the sign. Can't you see I'm blind? I have a seeing eye dog."
The bartender replies, "Since when do they give out Chihuahuas as seeing eye dogs?"
The man looks shocked, "They gave me a Chihuahua?"