Have your girlfriend kneel on the floor, with her back against the wall, and begin to give you head. Once she gets the rhythm going, push your entire penis into her mouth. When she starts to gag, there’ll be a recoil reaction. Then when she bangs the back of her head off the wall, she’ll be slammed back into the gagging position. If you continue to push and pump your penis into her mouth, this should result in a successful Jackhammer. Repeat as necessary.
For added suction, plug her nose once the Jackhammer has been achieved. This is pleasurable for both the man and the woman. This is also a variation of the air-tight seal.
Scott heard a loud and rapid thumping noise coming from his room mate's bedroom. He opened the door to see if there was a problem. He was relieved to tits bouncing, arms flailing and a smile on his buddy's face. Bill was face-fucking his girlfriend against the wall. Jackhammer!