Is feeling a girls butt a sin?

Answer 1

Oh, dude, feeling someone's butt without their consent is definitely not cool. It's like a big no-no in the land of common decency. So, yeah, if you're thinking about doing that, maybe just don't. Keep your hands to yourself, my friend.

Answer 2

whether it's a sin or not is up to you

but it IS rude and it IS harassment

unless you're in a relationship with the girl and she's ok with it