|Biff is just malicious, I don\'t think we have to take his definition serious. I also never had a negative connotation with grommets (and now groms). However, the term Betty was a bit depreciative ...
As for the usage in skater language, I can only guess that the term is used for the little ones because real grommets are small too: http://en.wikipedia.org/wiki/Grommet
Maybe someone else knows more?