Meanwhile his last game he was yasuo with score of 5/10. So I don't get why he thinks he can flame people in the first place?
The people who are most likely to flame are also generally likely to perform poorer than the people they flame. I'd imagine it has something to do with trying to scrape together some weak sense of pride in trashing other players, but it'll fall apart all over again once they inevitably get punished.
Second, what bothers me is he can say a bunch of disrespectful shit to me but I have to bite my tongue and say nothing back because I will get in trouble.
I have to ask you; what benefit is there to talking back?
You're not going to improve either of your scores. You're not going to improve the state of the game. You're not going to change their mind. All you're going to do is encourage them to flame you more, and then you get yourself caught up in a flame war that three other people have to suffer through. And all the while, both you and the Yasuo are going to be wasting time and energy on each other instead of focusing on the game, and you're both going to play worse.
Flaming people back is all negatives, no positives. There's zero legitimate benefit to it, and it comes at the cost of making the game worse for everyone and risking punishment.
I reported him but I highly doubt he would get in trouble but i bet you anything if I had say anything back, I would have gotten a 25 game chat restriction if not temporary ban or permaban.
...So, let me get this straight...
You're absolutely certain that you would've gotten punished had you spoken back (which isn't an unreasonable assumption)...
And yet you highly doubt that he would get punished?
You're going to have to explain this to me. I don't understand how you can simultaneously be certain you would've gotten punished and then doubt the likelihood that an actual, verifiable flamer would get punished.
I know nothing is perfect, but that's kind of not right that people can get away like that while I can't.
They don't. If you report them, they won't get away with it, period. Even if the player in question doesn't immediately receive punishment for their behavior, it adds up. As Kei143 explained, players have a behavioral history that adds up with each infraction, with more egregious offenses adding more immediate risk of punishment.
And flaming, as it were, is a pretty good way to fast-track yourself into being punished anyhow.
And besides, look around this sub-board for a while. People post here daily taking issue with being punished for flaming and other such misbehavior. Do you really, genuinely think that people can "get away" with things?