You have to pick:

I can avoid that word. The reason? There are ways around it, you see.

i could just shave my head. >_>

im assume its not painful
because magic

Oh, no - its painful. Its not like a guy with fie hair. Perhaps magic starts it, but when its on fire - its real fire.

Although that makes me wonder. Once it burns once, are you ok?

I guess in that case the stubble just catches on fire. Which makes shaving your head no escape either.

But what if you say cuz instead?
and once your hair starts on fire once does it grow back then start on fire again when you say the word again?
what happens if you say the word twice in a row? do you get burned twice as bad?

What is its fuel source?

I think "cuz" would still cause your hair to light on fire.

Your hair grows back at the normal rate.

If you say it twice in row, whatever's left of your hair starts on fire again.

The fuel source is your mom!

You secrete the fuel from glands, so ultimately the fuel source is your food. It takes as much metabolic energy as you'd need in the various WYR options where you get wings.