A person with an outwardly dominant, masculine, or aggressive personality, but who also enthusiastically takes on the submissive or "bottom" role in the bedroom.
"I'm tough, Mike! I never give an inch! I'm partial to taking a few though..."
"Ah, you're a real pipehitter."
The people who smoke crack and can therefore accomplish a difficult/dangerous/disturbing things because they only care about their next high.
Has been adopted by tier 1 special operations to refer to tough men who go the extra distance to accomplish the mission or rescue their fellow man. Doesn't really make much sense when used this way.
I'ma call a coupla hard, pipe-hittin' niggers, who'll go to work on the homes here with a pair of pliers and a blow torch. - Marcellus Wallace (Pulp Fiction)
"Just read about that Medal of Honour recipient. Absolute pipe hitter."