Ie, they shout "as if", often repeated by the action it is suggested they partake in, and exclaim whether they will or will not do it, and whether they love or hate it!
Can also be used if something is completely true, but you would like to draw more attention to it.
Jordyn: As If I can't go to LeedsFest! HATE THAT!
Lameass Are you going to LeedsFest this year?
Messy: No, but Tom is.
Lameass: Ahhhh! As If I hate that so much!
Monique: As if we're going to Paris in two weeks. Oh wait. We are.. LOVE THAT!
Made popular by the movie CLUELESS staring Alicia Silverstone.
Meaning: I'm definetly not going to do that / not into that/ don't beleive that / etc.