Getting changed for P:E

Is that a bra he's wearing?

Which movie is this?

At my school, you don't have to take P.E. if you don't want to. That's why, when I look out the school's window, and I see the P.E. kids doing pushups in frozen mud at 9:00 AM, I chuckle to myself.

Hey, is that when Hermione took Polyjuice Potion to look like Harry, and when she changed her clothes we can see her bra?