The Matrix: Neo versus Agent Smith. You know the part, right after Neo becomes The One and realizes he can see the code of the Matrix, and just starts casually slapping Smith around like he's nothing. The other Matrix films try to revisit it to various degrees, but it never gets as good as it was here again. This is, to my mind, the quintessential protagonist smackdown moment in film.
John Wick: John Wick versus Iosef. The whole sequence, honestly, but particularly for the way he dispatches Iosef himself. No unnecessary drama, no cinematic flourish, he just caps the little shit like he's nothing.
Bleach: Ichigo versus Aizen. The protagonist sets the tone by, instead of following the classic anime trope of "follow me so we can fight in a desert wasteland", instead casually grabbing the antagonist by the face and forcefully dragging him there. There aren't many better examples I can think of where the protagonist just comes right off the block letting the villain know they are not going to be putting up with any of their shit. There are certainly more one-sided beatdowns in anime, but outside of straight-up parody (OPM) I doubt you'll find many that feature a multi-arc antagonist getting this kind of drubbing.
Ed, Edd, and Eddie: Rolf versus Anyone. He just slaps their shit. There's nothing else to say.
