If dominate:
(Senpai name here) was playing something when he saw something and blushed automatically.
"Hey, what's that?" You ask and look at the photo.  It was you taking a bath! (For innocent people, use you doing a cute thing)
"Oh, so...." A small grin spreads on your face.

What do you do!?

If submissive:
(Senpai name here) was drunk and you walked him home.  During the walk, he looked at your body the whole time.

What do you do!?