The 'crabhammer' is quite simply a sexual maneuver.
1. the girl gives the guy a blowjob
2. the guy comes in the girl's mouth
3. the guy rolls onto back, and smacks the girl with the sole of his right foot, then his left
4. the guy rolls back up, and pushes the girl backwards (kinda rolling her upside down)
5. the guy sticks his index and middle fingers (of each hand) into the girl's ass, and pulls it open
6. insert scrotum into rectum
7. remove fingers
8. bounce up and down
9. Congratulations! you have completed the crabhammer
Guy: so in my dream I give this chick the crabhammer, and then she makes me a bologna sandwich as I jackhammer her while rawhide is playing on my stereo
Therapist: well... i guess that would mean that you have some feelings of latent affection towards her...
Guy: dude... are you fucking kidding me?