Just pick 
into him.
You can just walk up to him. AA, Q, AA with thunderlords and burst him for half health.
If he ever tries to E through your wave he isolates himself.
Wait until level 5 and then constantly ALL IN him. He can't do anything vs the bug.
The ban hammer is doing a very good job countering him in my games.
khazix to counter yasuo *LOL apparently you've never played against any good yasuos feelsbad
good idea.
however have you tried 
and 
?
because watching a yasuo simply implode is even funnier.
..... literally destroys yas.
i've played this matchup a few times in diamond elo. as a yasuo main, i can tell you it does not go well for kha'zix
