My own pet email peeve is emails with a subject line of 'link exchange request' or the like. They're spam, but spam that's often just individually customised enough to not always fall into the automatic spam filter alongside the Nigerian scams, genital enlargements and promises of a fabulous new career.
I mentioned this on Twitter and got a couple of other suggestions, including "Catchup for coffee" and "Moving forward" (ahem). But I figure Lifehacker readers will have other ideas. So which email subject lines act like a red rag for a bull, or send you racing to the delete key? Tell us in the comments.