This is a tough question. I certainly don't like being wrong but I don't mind being corrected in a discussion of facts, and if I'm proven wrong I'll more often than not admit it. Of course, not everyone feels that way and when proven wrong they do sometimes react in a hostile manner or just dig themselves a deeper hole to hide their heads in. Once it becomes obvious they don't see their fallacy, I'll just drop it because there's really no point as it's not even a discussion any longer.
A real problem, however, is when people start taking opinions as attacks or presume they are being presented as facts. There's really not even much point in starting in on situations like these.
Oh, and terrible spelling and/or grammar really bothers me. I will almost never correct someone for even the most egregious errors, but I will feel like tearing my eyes out with a rusty spork. (My biggest pet peeve is probably people who spell ROGUE as ROUGE.. argh) If you want to make a point or even sound somewhat intelligent, at least make an effort to spell the words you use correctly. If you don't know how to spell them, don't use them or if you have to use them, look them up in a dictionary first.