The act of taking a shit, or a dump, in the airfilter of someones car, so that whenever the owner turns on the air-conditioning, or especially the heating, the car will spew out the vile smell of shit in the airfilter.
person1: My girlfriend just dumped me... iu wish i could get back at her.
person2: awe, thats a shame, she had a really nice car. hey! i just had a great idea!
person1: is it an evil revenge scheme to get back at her?
person2: lets take a dump in her car's air filter! her car will smell like shit for EVER!
person1: yeah! great idea, we'll give her the best "filtercrap" ever!