More portraits have been shot of people high on something than not, I am pretty sure.
Yeah, it's underexposed and appears to be shot with on-camera flash. You can push the exposure up a bit, and it looks a lot better, but still not great. The flash is just not very fixable, it's just not gonna look that good. The background is pretty blah as well, possibly if you cloned out some of the mysterious crud back there it would look better.
On the up side: Well framed, to my eye. In focus. Good handling of depth of field. You've handled more than half of the technical bits of portrait shooting quite well.
I don't know the guy, but this feels like a pretty honest and accurate portrayal of some guy. There's no artifice here, no mugging for the camera, no lying. This is a guy, here he is. This is the man himself, no illusions, no dishonesty. If that's not portraiture, what is?