Spam
According to this article, the top ten deceptive email subject lines are:

• RE: Information you asked for
• hey
• Check this out!
• Is this your email?
• Please resend the email
• RE: Your order
• Past due account
• Please verify your information
• Version update
• RE: 4th of July

I don't understand how this can be. Most of the spam I get seems to orient around hot teen sluts, free samples of prescription drugs and mortgages.