Ya know Zim, in order to disguise yerself, you have to replicate more then the style, I think the girls will be able to tell you're an alien.

Bubbles will want to give you hugs (watch out, germs!).
Blossom will try to rationalize with you (like she's ever gonna understand anything you are screaming about).
And Buttercup will probably either want to kick you in the face or race.