Now, I know this couldn't have been a gaffer that did this to me...
I get invaded in Nightmare of Mensis, right before the door to
. This was my first time through this area and didn't know at the time how close I was to the boss. There's a small spiral staircase leading up to the landing in front of the door.
As I reach the top, from behind, I get attacked by the invader. No bow, wave, gesture or anything. Instead of rolling back where he can get a good drop attack on me, I roll forward. Pure panic and luck. Not skill. I'm guessing that was his plan, though, so he sidesteps near me and pulls out... of course... a cannon.
I turn around and jog to the spiral staircase without rolling. I hear his cannon hit the ground above my head. I charge in and start wailing on him with my Saw blade. My guess is that he didn't know about the cannon nerf, because it looked like he made the "out of ammo" animation. Then he died.
The lesson is: gesture before your fights!