To 'read' is to harshly critiqued/insult someone with your quick wit. To 'read for filth' is to really lay into someone and verbally (and often humorously), tear them apart.
MUGATU: i present to you... THE DEREK ZOOLANDER CENTER FOR KIDS WHO CAN'T READ GOOD! (unveils a model of the center for kids who cant read good and want to learn how to do other stuff good too)
DEREK: ..what is this?! a center for ants?!?! how can we be expected to teach children how to read if they can't even fit inside the building?!