A lecture about English
A linguistics professor was lecturing to his English class one day. "In English," he said, "A double negative forms a positive. In some languages, though, such as Russian, a double negative is still a negative. However, there is no language wherein a double positive can form a negative."

A voice from the back of the room piped up, "Yeah, right."

Attack Dog
A man wanted a big, verocious dog to protect his business, so he visited a kennel that specialized in attack dogs. The man explained to the kennel owner that he wanted the biggest, meanest, most vicious dog in the kennel, and the owner offered to take the man on a tour of the premises. After they had been walking for a few minutes, they came upon a large dog. He was snarling loudly and biting and clawing at the cage."He looks like he'd be a pretty good attack dog," said the buyer."Well, he's not bad," replied the owner, "but I have something better in mind for you."They continued walking around the premises, and after a while they found an even larger, meaner dog than the first. He snarled at the two men and tried to bite them through the wire on his cage."Ah," said the buyer, "This must be the dog you were referring to earlier.""Well, no." said the owner. "I have something better in mind for you."The men continued their tour. Eventually, they came upon a fairly large dog that was lying quietly on his side, licking his butt. He did not seem to notice as the men approached."This is the dog I had in mind for you," said the owner. The buyer was flabbergasted. "You're joking!" he exclaimed."This dog seems quite tame; he doesn't act at all like an attack dog at all. Hell, he's just lying there, licking his butt!""I know, I know," said the owner. "But you see, he just ate a lawyer, and he's trying to get the taste out of his mouth."