Of course, I don't think it's helpful to tell anyone you think they're going to Hell.
It appears that Jesus disagrees. These sure look like warnings to me!
NIV Matthew 23:33
"You snakes! You brood of vipers! How will you escape being condemned to hell?
NIV Mark 9:43-48
43. If your hand causes you to sin, cut it off. It is better for you to enter life maimed than with two hands to go into hell, where the fire never goes out.
45. And if your foot causes you to sin, cut it off. It is better for you to enter life crippled than to have two feet and be thrown into hell.
47. And if your eye causes you to sin, pluck it out. It is better for you to enter the kingdom of God with one eye than to have two eyes and be thrown into hell,
48. where "`their worm does not die, and the fire is not quenched.'
NIV Luke 12:5
5. But I will show you whom you should fear: Fear him who, after the killing othe body, has power to throw you into hell. Yes, I tell you, fear him.
NIV Luke 16:19-31
19. "There was a rich man who was dressed in purple and fine linen and lived in luxury every day.
20. At his gate was laid a beggar named Lazarus, covered with sores
21. and longing to eat what fell from the rich man's table. Even the dogs came and licked his sores.
22. "The time came when the beggar died and the angels carried him to Abraham's side. The rich man also died and was buried.
23. In hell, where he was in torment, he looked up and saw Abraham far away, with Lazarus by his side.
24. So he called to him, `Father Abraham, have pity on me and send Lazarus to dip the tip of his finger in water and cool my tongue, because I am in agony in this fire.'
25. "But Abraham replied, `Son, remember that in your lifetime you received your good things, while Lazarus received bad things, but now he is comforted here and you are in agony.
26. And besides all this, between us and you a great chasm has been fixed, so that those who want to go from here to you cannot, nor can anyone cross over from there to us.'
27. "He answered, `Then I beg you, father, send Lazarus to my father's house,
28. for I have five brothers. Let him warn them, so that they will not also come to this place of torment.'
29. "Abraham replied, `They have Moses and the Prophets; let them listen to them.'
30. "`No, father Abraham,' he said, `but if someone from the dead goes to them, they will repent.'
31. "He said to him, `If they do not listen to Moses and the Prophets, they will not be convinced even if someone rises from the dead.'"