I have two:
One, I was semi-AFK (I was at the keyboard, but eating, not using the controls.) Then, some guy runs in, as fast as possible, and I was cornered, due to the GREAT location I selected
Anyway, as fast as I can, I drop my fork into the bowl, press the button to whip out my naginata, and turn the guy into mush. He drops pliers, I'm happy, we were both on tag, yet he was the aggressor, so it's ok for me to kill him. That guy was completely unprovoked, probably just saw I was on Bmode. Well, maybe not entirely unprovoked, a week earlier, I was outside of Tanarthia, reading the forums when I heard the "failed" noise when someone attacks you and the attack fails. This was the same person, and I was fighting back, nearly killed him, then he runs (later I spare his life for a measly 20 plat, demn, I'm too nice.) ANYWAY, later that SAME day, this one guy, Kojilee, a newb also on tag (like me) runs up to me when he thinks I'm AFK, and casts magic bullet, sadly, for him, I wasn't, and turned him to mush before he gets out a second bullet.
The lesson of the story is, don't attack people who you think are AFK, because often they're not really AFK, and might kill you.