Straight from the USAKilts "Jokes" page:

A jumper cable walks into a bar. The barman says "I'll serve you, but don't start anything."---

A sandwich walks into a bar. The barman says "Sorry, we don't serve food in here."---

A man walks into a bar with a slab of asphalt under his arm and says, "A beer, please, and one for the road."---

A three-legged dog walks into a saloon in the Old West. He slides up to the bar and announces: "I'm looking for the man who shot my paw."---

A dyslexic man walks into a bra .---