Colossians 4: 6 Your speech should always be gracious, seasoned with salt, so that you may know how you should answer each person.
(2015-08-10). The Apologetics Study Bible (Apologetics Bible) (Kindle Locations 60779-60780). B&H Publishing Group. Kindle Edition.
I have heard so many stories of Christians being rude to non-Christians. If you are one of those people STOP IT! Witnessing will almost always sting, No one likes to be called a sinner, and there is no way to avoid all offense, but there is no reason to add offence.
Technically you are right when you say someone is going to Hell, but the moment you say it they tune you out, and will never hear your words about Christ forgiving sinners, and will make it more difficult to talk about the truth when someone else comes along.
Our words are supposed to be gracious (very polite in a way that shows respect)
and seasoned with salt (It preserves food, and makes you thirsty.) .
We are also supposed to have answers to the questions that non-Christians have. Being unsure how to answer a person is one way to almost ensure that someone gets cranky, The Bible tells me so, isn’t an answer that non-Christians will accept. If you get into that situation, don’t get cranky write their question down, and get someone to help you answer it.
If you are unwilling to become a genuine friend, leave them alone, don’t alienate that person from Christ more than they already are!