Five years later, but here's an alternate translation. Empty lines between panels. I'm not going to typeset this.
The guy is copying how the girl talks, like slime sleeper said (not the other way around like airy77 said).
"Not really" is reasonable for the phrase that gets used repeatedly, but I do think "not particularly" is better because it's more stiff and less casual.
Page 1
Shun: Good morning, auntie.
Auntie: Oh, morning, Shun-chan. Haven't you gotten taller again?
Shun: Not particularly...
Shun: A large spicy mayo bowl.
Lunch lady: Coming right up. You've got P.E. next? It's almost summer and the gym's really humid, isn't it?
Shun: Not particularly...
Friends: Shunta, do you like anyone out of these girls?
Shun: Uh, not particularly...
Friends: Ha ha, what's with that?
Friends: Wha, haven't you been saying that all day?
Teacher: Hey, take your seats.
Shun: Oh, that's probably because I hear it every day, huh.[/TD]
Page 2
Shun: I wonder what class she has right now.
Sign: Art room
Shun: Oh, hey...
Shun: You good?
Haneda: Not particularly...
Shun: Oh. Uh, er?
Page 3
Shun: Hey, Haneda... tests start next week, so isn't it bad if you're here painting?
Haneda: Not particularly...
Shun: Really? You've at least got some subjects you're bad at, right?
Haneda: ...
Haneda: ...not particularly.
Shun: Oh...
Shun: What was with that pause?
...
Shun: Ah, right.
Shun: I just realized today that it seems I caught your verbal habit... I even said it in front of my friends.
Shun: Your "not particularly..."
Shun: Crap, that gave her the ick.
Shun: Sorry, you probably hate that, right?
Page 4
Haneda: Not particularly...
Shun: Oh...