I'm not 100% certain if Koizumi is saying Haruhi will report Kyon to the cops, or if he will. My gut says he's talking about Haruhi. Either is plausible though.
Koizumi's pointing out Haruhi's jealousy. She'll call the cops if Kyon goes in while all three girls are in the changing booth, but won't if he goes in while only Haruhi is in there.
I know how to put on a YukataOh, really?
Then we'll have Yuki show usIsn't 3 people in a dressing room too crowded?Whaaat!?
You have to take off your underwear too!?There's special underwear that goes with a YukataHey Yuki, that's some pretty saucy underwear you're wearingThese are highly functionalWaaah~
My chest hurts when you tighten it that muchIf I don't, your top is going to pop outKoizumi, right now I'm engaged in battle with the part of me that wants to dive into the paradise behind that curtainI recommend you do that when only Suzumiya is in thereIf you do that now, she will call the police without hesitationSuzumiya-san, how do you put on a Yukata?You and Yuki are tiny, so it'll be fineRepeated this who knows how many timesJust a second, I'm calling a store clerk over