Aaah, come on ! The girls don't want to kiss me with the Edna's Mask... I'll never understand them !
I think I found the clothes that make you part of the cliques... When you're dressed like them they are more friendly with you (Having 100 % respect, of course). For example the Preps say something like "You're dressed excitingly well, Hopkins" or "My daddy can find you a job if you want".
All this is translated from french, so... It's possible that you won't understand what it is :
Nerds : Observatory shirt + School pants + Nice boy haircut.
Preps : Aquaberry shirt + Aquaberry pants cream color + Nice boy haircut.
Jocks : Sports vest + Gym pants + Bullworth team cap.
Bullies : Bullworth Polo + Jean pants.
For the Greasers I don't exactly know... Each one is dressed a bit different. I presume that anything in the "Final Haircut" fits. Tell me if you find it.