Why would a troll care if you agree or are giving the side eye? Their whole existence is simply to see if they can goad you into replying.

(And yes, you succeeded!)

"ok" is a dismissal of their existence. I'm explicitly saying that I dismiss them. They are trying to goad me into replying violently, as this is what confirms that they have an effect on the world. "ok" denies them any effect.

ok

lol

Some people expand this to "ok boomer" to really rile them up.