I've heard if it gets so many downvotes it'll become a low-rated comment

It is a simple way that someone gets a low rated comment. If someone is being toxic, didn't get a joke, or hating something, you simply downvote them and other downvote it, gets more downvotes than Upvotes, the low rated comment appears.

Oh, ok

It becomes low rated if they are toxic or if you are in the politics stream, have a different opinion

Lol ok

It depends on what it is like: "advertising" "repost detected" "not funny" "downvote" "that's fake" etc.

Got it!

it's just downvotes, if they have a ton of downvotes, then they're comment becomes a low rated comment

Ok!