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."

A prisoner with skills
Several years ago, Andy was sentenced to prison. During his stay, he got along well with the guards and all his fellow inmates. The warden saw that deep down, Andy was a good person and made arrangements for Andy to learn a trade while doing his time. After three years, Andy was recognized as one of the best carpenters in the local area. Often he would be given a weekend pass to do odd jobs for the citizens of the community.... and he always reported back to prison before Sunday night was over.

The warden was thinking of remodeling his kitchen and in fact had done much of the work himself. But he lacked the skills to build a set of kitchen cupboards and a large counter top which he had promised his wife. So he called Andy into his office and asked him to complete the job for him.

But, alas, Andy refused. He told the warden, "Gosh, I'd really like to help you but counter fitting is what got me into prison in the first place".