Oh ok. You are not God you just somehow have the right to speak for him.
Luke 6:37
"Do not judge, and you will not be judged. Do not condemn, and you will not be condemned. Forgive, and you will be forgiven.
It seems to me that telling someone that they are going to hell does little to make them want to listen to anything you have to say. Pushing someone away is not being Christ-like nor is it furthering your cause.
Add on top of that the fact that you have no idea who that person is who you just condemned to hell. All you did was react with condemnation toward sarcasm. Your judgement will forever be inferior to God's judgement because you do not know the soul of whom you condemn.