I Think My Teacher Is A Pervert

I'm kinda hesitant to tell the principal because, 1) she's our substitute teacher so she'll be gone in less than a month anyway, and 2) I feel like I'm the only one who finds it innapropriate, and I don't want him to think I'm the one twisting or perversifying the situation.

For the past few days, she has found a new way to punish students who arrive late to class or don't do their homework. She would call them to the front of the class, lift their sweater and start tickling their belly. She would sometimes poke their belly button, which, ew. Everyone starts laughing while I'm sitting there, feeling embarrassed for them, and praying this would never happen to me.

We're not kids, we're a bunch of teenage boys and girls, in the middle of puberty. I see the way guys react to girls getting tickled. She, of all people, should know about that.

The other day she wanted to punish this girl who was a little chubby. The girl was literally begging her to let her go back to her seat, but my teacher showed no sympathy. She lifted her shirt and started tickling her belly, and it started jiggling. The girl was red-faced and tried to squirm away. The girls were laughing at her while the boys had a dirty look on their faces.

I think it's wrong but I don't know what to do.