Brother in law just saw my boobs! [F]

I have my partners younger brother staying over for a couple days and he pretty much saw my whole boob hanging out of my singlet!

Im so embarrassed about it haha,
I was asleep and I sort of “felt” a presence in the room but wasnt sure, then about 5 seconds later I hear light footsteps and the door pulls shut! And sure enough I had one breast just hanging over the top of my singlet I was wearing!

I have a feeling he was just staring at me!

Now I dont know why the hell he was in my room in the 1st place, or how long he was there, but he has been avoiding me ever since , as soon as i walked out of my room, he jumps in the shower, and now he wants to go for a bike ride.

What should I do or say when he returns?
I dont know if I should be mad or not!
I feel like he has tried before too, like 2 days ago he tried walking in on me while i got dressed but I had a small dumbell behind the door and it slowed him right down.
Not this time! Lmao. How do I bring it up? Or should I forget it haha.