You know what really grinds my gears? When people make "Anonymous" comments on a blog.
I don't dislike it because I find it offensive or anything (although it's true people are more likely to be jerks when they're anonymous, which does not make a good statement about humanity). The reason it annoys me is that it is completely inhibitive to discussion, which is even more annoying when the Anonymous is asking a question. Or more likely, when there are multiple Anonymouses posting.
My replies always have to sound something like this:
Well, I agree with Anon@12:45, but I think Anon@3:45 makes a good point too. Of course, Anon@6:32 is being a complete jerk.
So if you comment on a blog, at least make up a name for yourself. Call yourself Joan of Arc for all I care, just please don't leave yourself as Anonymous.