Trendy, making clothes that are really trashy and making them look like designer quality, stylish, with accessories. It is something you are not something you can fake. Certified Junk people have an appreciation for wiggers, it goes back to the root of the word in some sort of way.
If Beefy wore a shirt that had holes in it and was clearly in dire need to be donated to your local garbage can and made it fashionable then he would be a guy who knew something about certified junk.