Why did you lose it? Because he was worried or because of something else?
Look, he's never seen her do exercise and he's slowly seeing new things about her. He couldn't resist moving her hair aside but also was genuinely worried that she might hurt herself. He couldn't say that directly so he chose to tease her instead.
Yaar, I don't know why I lost it at that. Of course, the concern was genuine and visible. But damn, that sheer alarm on his face, ki yeh kar kya rahi hai, it just cracked me up. I didn't give the why of it too much thought.
There was also some great comic timing through the scene, and it just got me. I kept pausing to laugh through the whole scene. 🤷🏻♀️