When a girl is giving a boy oral sexual intercourse, the boy finishes in her mouth. However, after this takes place, the boy will then take a straw and suck the semen from her mouth. From there, he spits it back into her face as she screams, "filter me!"
Kevin: "this head feels so good I think I'm going to come in your mouth. let me get a straw."
Kathy: "FILTER ME!"