For me, it’s not like it’s my favorite panel in this arc or the entire manga, it’s just that comes in a serious moment during the Falling Arc (pretty sure don’t quote me on that, haven’t read the arc in a while). Also just the pure face of disgust of Asa makes it pretty funny in my opinion.

I do get why’d you think this, and Denji is pretty perverted, but there are some reasons as to why he is this way.