Do you think when you tell yourself, "ok, I'm gonna go insane and just seize and start throwing things," that that's a good indication to when you involuntarily have a mental breakdown?

No, that's a good indication that you maintain the self-awareness to not have a breakdown.

It's when you seize and start throwing things involuntarily and without any recollection of your motives or reasoning that you've gone insane.

tl;dr You won't know when you're insane because you're insane.

No. You are aware of these thoughts, in fact you are telling yourself you are going to act in this manner. This is not involuntary.

Your mind plays tricks, you play tricks back

I don't really ever tell myself I'm going to do that, I just sort of picture myself doing it. That being said I never actually do it. I do think it's fair to say it's an indication of a potential mental breakdown considering I really only project that sort of mental image when I'm experiencing stress otherwise I probably would not be picturing such a violent image.

The idea that you are telling yourself this however does at least mean you still have a choice in the matter, and you can choose to get up and walk away from the stressful situation for at least a while to calm down. I still say though that if you are having this reaction fairly often you should look to make some change in your life to avoid whatever is causing you to stress out in the future.