It is her reaction to the news that the guy she fell in love with that morning--Hiroaki Kasahara--apparently enjoys dressing up in womens' clothing.
Three years ago, Jun tells her, Hiroaki was spotted walking around town wearing his sister's school uniform, with makeup and a wig and everything. At school they asked him what was going on--was it a dare, or a bet, or something?--and his only response was "It's my business, so butt out!"
That's as far as the new pages go.
This is what held me up for 7 months: I couldn't think of something that could have earned Hiroaki the contempt of all his classmates without it being super bad. I wanted something which was basically a major misunderstanding; otherwise I'd have had to make him a criminal or a lunatic or something.
So far I am undecided on exactly why Hiroaki was dressed in his sister's clothing. I am thinking that it's something seamy like a temp job at a transvestite bar, but I just don't know. It might be something entirely innocuous--he was in a play or something--or perhaps he either made or lost a bet with his sister, which was why he was wearing her clothes.
Or, even, perhaps he was tricked into it by his older sister: "If you want to get a girlfriend first you have to understand what it feels like to be a girl!" or some such, and he naively goes along with it, only to discover that his sister has been playing a practical joke on him.
The general upshot of the whole thing is that he's so embarassed by it that he just doesn't want to talk about it at all, hence "It's my business, so butt out!" This brusque retort coupled with his cross-dressing makes him an outcast.
Right now I am leaning towards the "transvestite bar" idea. (I got it from Yuzo Takada; he had the main character of 3x3 Eyes, Yakimo Fuji, working in such a bar at the beginning of the series.) It would be an excellent way for Hiroaki to make a fair amount of money quickly; and I then only need to know why he needed to that money. It sounds like I'm basically back where I started--not knowing why Hiroaki is in the situation he is in--but you see, I don't need to know that exact detail right away, because it will be many many many many pages before that is revealed...and it will be the revelation of this fact which redeems him in the sight of his peers, at least enough for Megumi to begin dating him.
His classmates, discovering that he works in a transvestite bar, won't pursue the issue any further than that and just assume that he's queer as a 300 yen bill, and hence ostracize him. (Are you kidding? Even American kids torture their peers for being "different" in much less extreme ways than that!) So, this is why Hiroaki warns Megumi not to talk to him, for her own good.
I think that works.