These insults from Ask Reddit are brutal.
1. If there was a competition for failures, you would get second place, because you can never win.
2. You’re the reason the gene pool needs a lifeguard.
3. You are an inspiration for birth control.
4. It’s impossible to underestimate you.
5. I’m jealous of people that haven’t met you.
6. You’re the kind of person that history forgets.
7. I don’t hate you, but if you were on fire and I had a bucket of water, I would drink the water.
8. If God doesn’t create ugly people, who created you?
9. I hope your internet gets cut off.
10. Your birth certificate was an apology letter from the condom factory.
11. You’re an oxygen thief.
12. I don’t have crayons or a sheet to explain it to you.
13. When you get home, I hope your mom runs out from under the porch and bites you.
14. You’re the result of an empty bottle of tequila and a broken condom.
15. You have a good face for radio.
16. My only luck in life was not being you.
17. I have seen better looking heads on boils!
18. I’ve forgotten more than you know.
19. Your grades say marry rich but your face says study harder.
20. May all your steps be plagued by the sharp pain of a Lego brick.
21. You will die of irrelevance.
22. Your opinion is so worthless, I do not care enough to even be offended, as that would require a shred of respect.
23. You are an appendix: nobody thinks about you unless you’re causing trouble, and we’re all just fine without you.
24. I thought Neanderthals were extinct. Archaeologists will be thrilled to hear about you.
25. You have delusions of adequacy.
26. You’re the reason your mom swallows now.
27. Oh honey, you’re not pretty enough to be this stupid.
28. Mr. Rogers would be disappointed in you.
29. Every time you talk, I hear your parents disappointment.
30. You are in my league. 
