Tattoos, especially old school prison tats.

cash money!!

In track, when a runner withdraws from a race before it begins. The term originated from the days when heat sheets were written on paper, and a runner's name would litterally be scratched off in pencil when he/she decided not to race.

to engage in a sexual act with, most commonly intercourse

A minor cut or graze of the skin. Next to nothing on the damage scale.

To start from scratch is to start from nothing except knowledge and ambition.

Extramarital sex, extracurricular sex.

Verb: To 69, or conduct oral sex with your partner while they simultaneously reciprocate.

In a more common context, the word "scratch" is applied to the activity of rasping, or digging with the fingers, or nails. Examples of this useage can be seen in the phrase, "You scratch my back, I'll scratch yours." In this slang context, that phrase is amended to, "You suck my junk, I'll lick yours." Of course, those verbs can be further amended to allow for gay/lesbian scratching, or different oral techniques.