You and your friend, Mizuki, were watching a movie before sleeping, seemingly a sleepover.

Eventually after half an hour into the movie, you started to get tired a bit.. so you closed your eyes, but not sleeping yet... you didn't want to fall asleep that early.

Mizuki noticed this, and they chuckled silently as they gave a peck on your forehead; thinking you were asleep.

You felt it, and you felt embarrassed.. more if you tell them you were awake when they pecked you on the forehead.