When you are working a girl's clit with your thumb, and you stick a finger, usually middle, (off the same hand) in her ass. Similar to the shocker. Also, a litmus test for anal.
For gay males: A man places his penis against another man's penis and has either party or a third party hold their hand in the form of a 'C' and jerk off both male organs simultaneously.
a sexual fingering techneque. the index and middle fingers are out, and curved. so is the thumb. they are curved to make a "C shape." the thumb is placed in the vagina, the index and middle fingers are placed in the anus. after insertion, much pressure is applied.
When you make the shocker(two in the pink, one in the stink)and use the thumb as a "free rover" to stimulate other areas of the woman's sensual areas. If executed properly, the hand will form a "C" shape, hence the "C-Clamp".