"I can't see any reference to underachieving in the lyrics"
This is what I see as a kind of reference to under-achieving by calling out and insulting people who work harder: "Let’s have a toast for the jerkoffs / That’ll never take work off." It seems to me that the voice is therefore showing contempt for over-achievers and, by taking the rest of the lyrics into account and the fact that I've met a lot of people who despise fellow employees that work harder than they do, I leap to the assumption that the voice himself must be like one of those under achieving dicks.
"The main speaker is most definitely talking about being a high-achiever."
Others have said similar. I think the voice thinks he's "all that," but in my opinion someone who feels a need to say things like this are decidedly not and therefore I don't agree that the voice is actually a high-achiever. It seems more like the speaker in the song is trying to justify his bad attitude by just declaring that he's the smartest/best person in the room and everyone else are idiots (as if by virtue of him saying that, it makes it true - because after all, he's so damn much better than everyone else!) - but that is not the mark of a truly intelligent person, IMO, and that's probably why I interpret the speaker as just being a dick. If he tried harder, tried to teach and support and didn't attempt to chase the girl away, he could be the smartest guy in the room. Instead, he just chases people away to make room for his ego.
Anyway, you could be totally right. I'm just trying to clarify where I was coming from. I would posit that in the case of interpreting art, there's no one truly "right" answer anyway, so it doesn't really matter - and maybe that's the point. :)