1. Always correct others when they are wrong.
2. Avoid “win-win” outcomes and instead rub in an opponent’s loss.
3. Surprise people with bad news.
4. Overpromise.
5. Underperform.
6. Let others rely upon your word, and then renege on your commitment.
7. Use sarcasm.
8. Spread rumors.
9. Boast.
10. Lie.
11. Belittle people.
12. Respond promptly whenever you are angry.
13. Routinely question the motives of others.
14. Be too busy for others.
15. Don’t respect their time.
16. Make loose allegations.
17. Be uncaring.
18. Ignore common courtesies.
19. Don’t return letters, calls or email.
20. Engage in personal attacks.
21. Exhibit cruel and senseless prejudices.
22. Openly enjoy the discomfort of others.
23. Embarrass people.
24. Don’t keep confidences.
25. Claim undue credit.
26. Be hypercritical.
27. Be indiscreet.
28. Be crude.
29. Look down on people.
30. Kiss up and kick down.

Note the common thread in the above. All may be summed up in one word: inconsiderate. Being considerate takes time and work. It doesn’t come naturally.