American slang for a square, a nerd, a dork, a mooncalf, a wheyface. Pronounced with the h vocalized. Rarely used as a verb (in much the same way as "fool"): Are you herbin' me? Most commonly heard among school children of the north eastern U.S., who are attempting to be fly gangstas. "Herb" is also slang for "marijuana", but its etymology probably lies in the common name "Herbert". Herbert is a pretty nerdy name, and is certainly not as cool as Rocky or Butch. Also, the h in Herbert is vocalized, just as in the insult "herb". Common American usage is to pronounce "herb" as erb.

While "herb" means "person who isn't very cool at all", it's rarely directed at those outside the user's social circle. That loser kid your cousin is dating is a herb; the smelly boy who you would never, ever talk to is a freak. "Herb" implies that you're in the same group as the person you're insulting, or at least know the same people. It's not a strong insult, often used jokingly, though it carries a connotation of disparagement. Not quite disgust, not an indictment of sexual immorality, "herb" is used in the similar situations as one would playfully say "dork".

The origins of "herb" are very mysterious. It appears to have first seen use in the early or mid-1990's, and it has not spread much beyond the Atlantic seaboard. Sid passed me this link: Since I was one year old in 1985, I can't vouch for Herb the Nerd's popularity as a Burger King mascot, but I guess it makes sense.