A croc is a girl who is either ugly, gross, fat, trashy, slutty, or any combination of the previous.
No one respects Croc shoes because they are useless shoes.. Just like no one respects girls with any of the previously listed qualities.
A true croc is also a girl who is 'walked on'- just like the real shoe.
Cody: Wow, look at that ugly girl funnelling vodka.
Nate: She's a total croc!
Cody: The only reason that 28 year old is dating that 16-year-old trailer trash slut is so he can get laid whenever he wants.
Nate: Not my croc, not my problem.