As someone who has and still does disagree with you on a great many things, thanks for the terrific advice--not in how to deal with you :) but in your haughty declaration that you know some things that will help others to be better Objectivists and live more proudly, happily, and consistently. Your list of sins is, indeed, a list of which anyone who values reason should take heed. In particular, I plan to take heed of them and rid myself of some self-destructive habits, thought processes, and ideas.
1) "Gratuitous and premature umbrage-taking."
Ever since I've accepted Objectivism, I've found much more confidence in my own judgment, but from time to time, I am offended by merely opposing viewpoints. I'll keep my pride, and I think I'll try to come away with an attitude more firmly resolved and less flammable when it's only my ego, not the ideas, at stake.
This is one I don't think I've ever suffered from but have always--even when I was a Christian--despised in others. Your summation of that ambiguous trait I had merely identified as "self-absorption" (as opposed to "self-confidence") was right on the money.
I've seen new and seasoned Objectivists violate this precept on many occasions, and it's disturbing to see people otherwise dedicated to reason simply drop all context and become hedonistic narcissists.
While discretion (and diplomacy) is occasionally the better part of valor, the moral man knows when to take a stand and say A is A. This is and will remain one of my primary moral goals--never to back down but only to be inflammatory and caustic when it's a proper (intellectual *and* emotional) response.
While you might not have meant all those things, I think Objectivists, old and especially new, would be wise to start here for some introspection.