A bad headhunter finds your email address online, and cold-call emails you a random position that doesn't match your interests at all.
A *terrible* headhunter gets passive-aggressive about the fact that you ignored the previous email, sends you an "oh, didn't you get my previous email? Let me tell you about the position again" followup, and then gets defensive when you call them on it.
(Yes, I know -- first-world problems. But I don't believe I've ever gotten so angry at a recruiter before -- I wound up letting loose a full-bore flame this time. If she writes back yet again, I'm going to have to find someone at the company to complain to about harassment...)