If ever you are in 1st in a race and there is a lot of Fire Guy activity, there's an easy way to avoid them. Just pick up an exploding chicken or TNT monkey, and throw it back as soon as you see a set of crosshairs turn red from a Fire Guy closing in. You will destroy the Fire Guy and avoid damage completely!
You can also shoot it if you are the gunner of a clashed car, but this proves difficult with some weapons.
Also, this works with any power-up, but it's most convenient with insta-kill power-ups like Fire Guys.