Spank her

You can't resist the invitation, what with her ass pointed outwards like this. You rub your hands together, walk over, and start spanking her exposed behind until it's as red as her face is.

"Wait, stop, what do you think you're-"

* smack *

"-doing! Ahh!"

* smack *

"Don't..!"

* smack *

With every slam her asscheecks give an appreciable wiggle while the girl lets out a squeel. When you're done, you give her butt a good grab. You can feel how muscular she is, even if that didn't prevent all the wobbling.

Judging by how red she is all over now, cheeks and asscheeks, you contemplate whether she's learned her lesson by now.