Derived from 9gag, defined as "a horrible excuse for a website than sic mainly incorporates stolen materials and ideas from other legitimate websites. 9GAG is also a large source of child pornography."
A 9gagger is someone who creates and/or promotes and/or enjoys such websites. Colloquial usage refers to anyone who is slimy, dishonest, disgusting, or a pedophile.
This egregiously gross website might appeal to creeps, pedophiles and 9gaggers, but never to normal people.