Hardcore is a term used to justify some dislike. This term is often used by those who are not "hardcore" but want others to believe they are. Bands are often critized for being "not hardcore" because they are vastly more successful than the people bitching about them.
Steve: That band sucks ass they arn't even hardcore.
Brian: Your just pissed cuz they don't live in their parents basement anymore...like some people i know. (looks at Steve and winks)
Slip Knot is a "band" that teenagers listen to so their parents will freak out. Their "music" is in fact soo bad that the band members openly admit they are not musicians. So if your a teenager and you want to punish your parents and feel bad about the world; paint your fingernails black and listen to slip knot.
Slip knot is so god awful that when I hear it I contemplate using a slip knot on myself!