So, last night I forgot to turn off my turn signal and nearly crased because of it.Who's fault would it have been? To me it seems like the other driver should have taken into consideration "Defensive driving".

 

I imagine signaling incorrectly would fall into the same category as failing to signal.

On the other hand, if the person was following too close, thinking you were going to turn off in front of them, they could be equally responsible.

Stuff like that tends to depend on the situation, not just the basic details like you've provided.

 

Depends on who had the right of way.

If you had the right of way it doesnt matter what your signal was doing as they have to yield to you. Of course that doesn't mean you should expect drivers to grant you the right of way.