I stumbled across something today that reminded me of this one. It goes back several years. Spam Arrest - an anti-spam company (yeah, right) - not only spammed their customers, but they also took their customers' email lists, and spammed them too.
It was a despicable thing to do. Loads of people were up in arms about it. Spam Arrest then tried to rewrite history by asking webmasters to remove the negative comments to try and whitewash the fact that it had ever happened.
We all make mistakes and an apology is usually acceptable, but what they did was IMO unforgivable. AFAIK, most webmasters (including me) refused to remove their content about the Spam Arrest scam.
Sure, we all get 419s and other rubbish but when an anti-spam company deliberately spams, I don't think it's easy to forgive or forget.
What's the worst spam you've received?