Totally tsundere. Also, I seem to have forgotten what you say when clothes are too tight... biting into your skin, maybe? Though that's more for accessories rather than clothes...
"Riding up" seems to be a common way to describe the situation in panel 3. Sources indicate it's caused by having a swimsuit that is too large/loose though.
Why would I wear something like that... Are you stupid? Do you want to die or something?~A few minutes later~School swimsuit?Well...KazamiI wanted to see you happy, so I put it on for you!Ah...! It's biting into my butt...You did say you really wanted to see it...