Grundlebate
A highly stimulating sex act whereby your sexual partner tightly, but gingerly, pinches your grundle while you furiously and feverishly masturbate yourself. To perform properly, your mate must pinch the grundle between their thumb and forefinger and must tug this fleshy area back and forth and up and down in rhythmic and synchronous harmony to the recipient's stroking and beating of their turgid cock. Said act is known for explosive orgasms but can result in a very sore taint if performed too frequently.
Carl exploded in a body quivering orgasm after his girlfriend helped him get off with a little Grundlebate action. She tugged a little to hard though and Carl's taint was a little tender to the touch the next morning.