Just how socially stunted and entitled do you have to be?

My (21) younger brother (18) grabbed at his crotch in front of me the other day and it made me uncomfortable. We were mid conversation and he started grabbing at and shifting around his crotch while holding eye contact with me. He wouldn't stop staring, so I looked away as I continued talking.

In the moment, I got a little dissociative, staring at the wall while my hands continued doing my hair on autopilot. I didn't process the fact that it was odd to me until almost an hour later. I'd have asked him to just step away to sort himself out if I had been fully present in the moment.

It's hot where we are right now, so I understand why it might've happened. Plus I don't know what his current norms are. He had been home from uni for all of 2 hours before this happened. I'm aware I shouldn't make assumptions. I just don't wanna project my existing discomfort about him onto the situation.

We're not close enough for him to do something like that. We hug like twice a year and barely talk, even if we're in the same house. He's had poor boundaries with others in general since childhood, but this was different to him trying to convince me I should get naked while playing games when we were younger, or staring at places I'd rather he didn't during my teens and up.

We're adults now. And I still hate it here.

I already worry about him being alone around our sister because of our history. If he normalises things like this around her next, it could be bad. But maybe I'm reaching.

I don't have another guy's behaviour or opinions to reference to determine what's normal here. Our father was/is/forever will be the worst. I don't talk to him.

I don't want to make my brother uncomfortable by bringing it up to him, or asking for input from anyone healthy we both know. Though, maybe I should bring it up to him directly, considering the fact that he was fine staring at me like that while he did it in the first place.

I have one good male role model, our uncle. Even though he's never done something like this around me, I've also never been around him during a heatwave, so he still might not even be a fair point of reference.

Either way it was weird and inconsiderate. A whole summer with him is too long. I've never been comfortable living with men in my space. Part of me doubts I ever will be.