I can't see anyone doing that to me besides one of those really red-cheeked frat boys or edgy teens that always try to dunk on me to impress their friends. I would explode, I guess? Like wOW, you got me. You did a hand gesture that makes you look like a fkn disgusting piece of trash. A true lord of chaos, that's what you are. We've all been put in our place now.
But really, even those kids aren't usually so bad that they'll try to use Nazi imagery.

Realistically, I'd probably be able to do exactly nothing if it happened in passing besides think, "Oh, absolutely not." But hopefully, if I saw someone openly being a nazi I'd film them with my phone and get it online so that maybe they can be identified. Would I want to smack them? Yep, but I'm not going to pretend I'd actually do it. Smacking people isn't a reflex of mine. Plus, if I had any time to think about it I'd settle on not going to jail for just smacking a little alt-right b i t c h. I think me not being in jail would actually make them madder than smacks.