Why are his pants unbuttoned though?

Came here wondering the same thing.

What is this image from? Is there context to explain his pants being open?

It’s from the first nightmare on elm street movie, he’s trying to stay awake so Freddy doesn’t kill him.
He has the wrong idea about Sadako?
He was watching a Jazzercise tape.

That’s Johnny Depp in Nightmare on Elm Street, and he’s actually wearing a crop top.