If you aren't Heat, then maybe you are Electricity.
I will not be taken lightly
This title could be a play on words, referring to electric-powered lights.
Leave me alone! For I am warm and content in my prison.
Touching live currents can result in a painful (or lethal) shock. It is warm because electric potential energy can be converted to thermal energy (also, metals with high resistance will heat up when current passes through them). As for the "prison", this could refer to wires (which contain current), batteries (which contain voltage), or capacitors (which contain charge). Yes, I realize that's not an accurate description of electricity, but it's a riddle, ok?
I am the very essence that defines you, you would be a clammy fool without me!
The human nervous system, as well as the heart's ability to beat on its own, relies on electrical signals. Without those signals (e.g., brain failure), a person would be dead, resulting in a clammy, mindless corpse.
And yet you use me, expecting that I will not react coldly to your presence.
Electricity powers almost all of our technology. The word "coldly" means "negatively" or "harshly", as in a not-properly-grounded electric current that shocks a person who touches it.
Abuse me, and I'll burn your stupid house down.
Faulty wiring can result in sparks or overheated metal, which in turn may result in house fires.