I'm a bit late with the list, here it is:
Nerds
Beatrice: I don't know what this means...
Bucky: What the... Huh?
Cornelious: But I don't understand...
Earnest: That's incomprehensible!
Melvin: I feel like my head is going to explode!
Thad: Sorry?
Bullies
Davis: I don't get it...
Russell: Russell... Confused!
Tom: I have no clue what's going on! Like, none at all!
Troy: What? Words?
Wade: What is... huh?
Jocks
Bo: What the? I don't understand!
casey: I don't get it!
Dan: What the?
Juri: Uhm... What is... Uhh... What?
Kirby: Sure that's... Yeah... What?
Luis: Wait... Wait a minute...
Mandy: This is just so confusing!
Ted: Time out dude! That scheme is confusing!
Greasers
Hal: This makes my head hurt!
Johnny: Woah...
Lefty: This is messing with my head!
Lola: Uhhh... What?
Lucky: what the heck is that?
Norton: My head hurts trying to think it out!
Peanut: What? Huh?
Ricky: I don't get it! What the hell?
Vance: What is goin' on?
Preppies
Bif: I don't even know where to begin.
Bryce: You commoners make no sense!
Chad: What is going on?
Derby: What the heck is going on?
Gord: Can someone help me make sense of this?
Justin: What is going on?
Parker: Uhmm... That doesn't make sense!
Pinky: I don't get it!
Tad: Ok... Yeah... What?
Dropouts
Clint: Woaaah! Let's take it down a few notches!
Duncan: This, makes my brain hurt real bad!
Edgar: What's this crap now?
Gurney(1st quote): Uhhh, what?
Gurney(2nd quote): Wait... my head hurts!
Jerry: Uhhhh...
Leon: Man! What's goin' on now?
Omar: I must.. Uhh... Argh!
Otto: I just don't get it!
Zoe: Huh... Confusing.
Non-Clique
Angie: Hmm! I don't get it!
Christy: wait!
Constantinos: I just don't understand!
Eunice: Huh? What?
Gary: What's going on?
Gloria: I am positively, flomaged at this point!
Gordon: I don't get it! Huh?
Ivan: I just won't go. I'm not sure I'm getting all of this...
Karen: Uhm... I'm confused!
Lance: I'm not even gonna pretend I get what's going on!
Melody: Ay ay ay!
Pedro: Uhm... Err... Momma?
Pete: What the hell is going on?
Ray: This is confusing on so many levels!
Sheldon: This is weird!
Trevor: I'm bewildered!