A man with a Labrador Retriever goes into a pub and sits down at the counter. Barman says "You can't bring that dog in here!"
Man says "But this is a guide dog!"
Barman says, "Well, OK, then I suppose it can stay."
After a while, the man and the Labrador Retriever get up to leave. As they're going out the door, another man with a Chihuahua is coming in.
First man says, "The barman won't like you bringing that dog in here, but just tell him it's a guide dog and then it'll be OK."
Second man looks dubiously at his tiny Chihuahua, thinks a few seconds, thanks the first man and goes on in.
Barman says, "You can't bring that Chihuahua in here!"
Man stares straight ahead and exclaims, "What! They sold me a Chihuahua?!"