Spam. It's the e-mail you don't want, but is sent to you anyway. In fact, Spam has been around since before the Internet and e-mail became mainstream. They even celebrated the 30th birthday of the first known Spam message last year.
I've been able to watch the evolution of Spam fighting techniques over the years, and while I understand the need for inbox protection from nefarious spammers, I'm fed up with the laziness of e-mail users.