It will take a lot of effort, but yeah, I guess you could be a hacktivist that way. A smarter approach would be to leave little Arduino proxies or something in public Wifi locations, so you could do it all remotely. And then, going to the logical conclusion you arrive back at DDoS from other people’s hacked computers, which is a time honoured cybercrime strategy.
It would take a lot of time and it’s still not going to sink Reddit if it’s just you, though. Honestly looking at Twitter you have to do ridiculous shit to a big monopoly-ish network service to make people leave it. Like, more than Elon already did.