I've never come across 'antifa' and likely won't but the first thing I would say to them is "ok, who would like to take a stab at defining fascism? Anyone? Don't google it, that's cheating, come on -- you've devoted all this time and energy to being against something let's hear what exactly you think it is."
Crickets.
Then I would explain to the nimrods that the goals of the party they affiliate with -- most notably disarming the public and consolidating power with a large, overbearing government -- much more closely resemble fascism in general and National Socialism in particular than the relatively libertarian policies of the president they rail against.
Then I would commence with the noogies and atomic wedgies and -- if God willing there was a toilet nearby -- swirlies. Bonus points if I had the presence of mind to take a shit it in before hand. Fuckin dipshits.
MORE TITTIES PLEASE.