I've seen lots of anime character do this, and I'm wondering if people in real life do this with every sentence or if it's just a little quirk which characters have.
It's a contraction of です/ます. It's just slightly less polite. I definiely heard people in real life use it, maybe not every sentences but mainly young men uses it.
I will talk mostly of っす as a contraction of です because I'm not that familiar with the ます one (except in expression like ございます). I often hear that one in casual conversation and it can be use with every sentences (like you would use です) but not by everyone.
Like, I know at least two kind of people that would use it: - Kids that are a bit "bratty" and "rebel" (close to anime character) - People that don't want to be too polite but don't want to be completely casual either
The difference is really their entire way of speaking and tone, so it's not just っす. Also using っす is a kind of a "safe zone" for some people? Like there are some people that are too used to polite speech and use っす as intermediate instead of going fully casual. The opposite also exist, casual people that use っす to meet up with people that are always on polite speech mode.
But beware, for some people, it's also kinda "vulgar" too. I got scold by a friend because of that. Well, maybe not scold but it was like "Why are you talking like a brat? Don't use that". And as the same time, I know some people that just use it everywhere.
So yeah, it's real but not everyone use it (and not in every situation)
@Shamugan, I was aware that it was a short casual version of です/ます before but I didn't know there was more to it. Your explanation was really helpful, thank you!