These 'Callout Cards' from That's Not Cool toe the line between passive-aggressive hate notes and proactive nasty e-mails. They blend witty one-liners with cutesy icons and a clean speech bubble layout to get your point across succinctly and sarcastically.
I've selected ten of my favorite 'Callout Cards' in the gallery above. Some gems: "Sorry I waited a whopping two minutes to respond to your IM," "Congrats! With that last text you've achieved stalker status," and "I'm looking forward to you clogging my inbox this weekend."