a derivative of the "Alabama jackhammer"; a standing "69" in which the woman is upside-down performing fellatio. Once the man senses the nearing of the orgasm he performs an Alabama jackhammer like maneuver in which he belly-flops (still in the 69 position) onto the bed/floor/table, etc., and slams his penis into the back of the woman's throat releasing a heap of semen into the bronchial tubes or esophagus of the woman
"The other day I was 69in'... but standin' up...and when I thought I was gonna cum I pulled a Birminghambelly-flop on my lady and she went "GAH!" and I went "nnnguuuuuuuuuh!!!"
An exercise in which one sprints the length of a football field, dropping at the marked 5 yard intervals to to a push-up. Typically belly flops are assigned as a punitive measure.
Football coach - "Alright, since you clowned around so much during the game that we lost, you get to do belly flops right now until I get tired!"
football team "Aww fuck man, this is gonna suck..."