Most duos I met sucked and fed. But this is not my point and I'm totally fine with that. The most annoying part of duos is: the two players will end up being toxic together even if there is only one player being a jerk at the beginning.

nono. ALL duos suck and feed in ranked. and its not just you.

"bro let my friend mid he is really good"...

is 200 elo below the rest of us...has 10 more losses then wins, proceeds to feed mid badly...blames the jungler, then he and his friend afk in base and make swastikas with wards.

You're only noticing the bad duos because they stand out. There are many more duos that you've played with that you don't notice because they aren't doing anything unusual.

Whenever you know they're a duo, it means they're trash.

How about you stop being ignorant. And realize just because a couple of duo's "suck" doesn't mean every single duo is bad. I duo with my friend and we usually do well, we have our matches that do bad. Just stating the fact that not all duo's "feed." Also, there is a high chance that they aren't dying on purpose.