I can only answer for myself here, of course. I enjoy some (not extreme) sexual pain, and I’ve done and enjoyed a fair amount of peircing and cutting. FWIW, I’m not trying to externalize inner pain, I do it for much more positive reasons (but that’s a whole different question to answer).
I have a fairly high pain tolerance in general, and the ability to control reflex reactions to sudden pain, but I by no means enjoy day-to-day injuries. Stubbed toes and paper cuts elicit the same amount of swearing and limping from me as from anyone.
Part of this difference is context, of course. Everyone interprets sensations differently when aroused - someone brushing by your butt on the subway doesn’t feel the same as a lover running his/her hands over you lightly.
For me, at least, much of the difference is damage done to my body. When I dislocated my knee (several times) or when my ovary had twisted around to cut off its own nervous and blood supply - these were very, very painful. Knowing that something horrible and destructive is happening to your body makes you want it to stop, and makes the pain much worse (again, IMO).
Volutary pain, however, I’ve always done with someone who I trust to not injure me (in a sexual context), or to only leave marks that were planned and that I consider beautiful (in the case of scarification and peircing). Being able to relax about harm has always allowed me to interpret pain as straight sensation - overwhelmingly powerful, but with none of the instictive revulsion and, well, pain, that injuries produce. It helps that, especially for scarification, I’ve taken lots of time to mentally prepare myself.
To summarize an already too-long post: IMO, masochists experience everyday pain the same way everyone else does, and whine about it as much. I only enjoy pain in special contexts which are both safe and rewarding in some way.
(Who also thinks it was a good question.)