Metrosexual is part of it, but this herbivore thing has a much broader scope of influence than that, as it also extends to ones romantic preferences and attitudes toward the opposite sex as well. Namely being that one can "spend the night" with a girl without touching her, or "has no interest in dating" for economic reasons, and other such things.
The fact that he won't even willingly grope his female companions, even though they want him to, puts him into that category. Plus he's chummy with his mom, and generally doesn't know what his future holds after graduation. (EDIT: Oh yes, plus he's not very competitive with his grades or his place in life, except in ways to protect those dear to him.)
For all we know, he might end up still living with his family for a while longer while going to university and even after that... that is, if he doesn't get sucked back into the affairs of the youkai world. Which is looking more and more likely with each new story arc.
If you discount the items that fall under the "metrosexual" term, but apply the rest of what the herbivorous male is by Japanese standards, you pretty much get Tsukune. Though unlike the typical herbivorous man, he does have a girl in mind to eventually marry and spend the rest of his life with, plus the fact that her family is LOADED also helps. So the decision there is pretty easy.
Though for this I'm restricting my opinion to Tsukune's romantic life as being herbivorous, because he's passive in his romantic endeavors, he almost never makes a move to be romantic with any of the girls except Moka, whom of which is too dense herself to see his advances on her. So we see the other girls being "carnivorous" in their pursuit of Tsukune, in that they are very aggressive with their ambitions of getting him as their lover.
There's a whole lot of other things going on that describe this type. I recomend going to
Sankakucomplex.com and looking up their news articles on herbivorous males and wedding and relationship trends in japan to really get how this term is used. You got to
think Japanese in order to understand it they way they do.
Many japanese females are frustrated about this, but then again, they all want rich husbands too, which they have no hope of getting anyway in today's economy. So Tsukune is rather a lucky man, even if he is passive for the most part, to be entertaining the attentions of so many potential mates.