Surely what you really mean is "What makes you angry?" What arouses wrath? Or even just irritability? "What makes you mad?' - Madness is another word for insanity. A mad person is one who needs psychiatric treatment.
But getting back to 'What makes you mad?' in the sense you probably mean it.
It happens when the thoughts in your mind - which have taken on an identity and feel they are an entity in their own right - are thrown into fear. Our mental image of ourselves, our self-image, is exactly that: an image, not the REAL us. When our self-image's beliefs are suddenly challenged there comes the real fear that we are being destroyed in some way. The moment there is even the slightest thought that our self-image is not right in some way (e.g. not getting its own way, is frustrated, told it is wrong, et cetera) the fear sets in.
All negative emotions are simply another way of fear expressing itself: flight or fight. The fight may be physical, or just a verbal argument, or even the insistence of having the last word. Some one tore a piece out of your ego. You must restore it immediately or be the lesser for it.
Of course, the REAL you is not mad (angry) If you think this is a log of hogwash, by the way, just observe your own reactions when you are tempted by something the real you knows is not good for you. Observe the conflict. Witness the inner turmoil and emotions arise as it (the ego) feels it can't get its way.