The first thing I think of is power.
Larger clothing: Pumping up and deluding yourself to how much power and space you actually take in this world. Like, feeling like a 'big man' even though you may not be in any sense at all. Or you may be a big shot.
Too small clothes: Seeing oneself as smaller and lacking power and clout.
This actually fits in with what you were saying, boom. Kev feeling rather powerless, so he goes shooting a bunch kids with a crossbow.?!
Well, that is how I have always translated it when it didn't seem to be about sex or pure body image (I AM not fat, dammit!).
Those little punks A.K.A. rappers trying to fill as much bloody space as possible, even though they are just skinny little jerks.

Like, look at me, I'm the shitza and BIG. pfff