A firebender not being careful with his bending.
Firebending more commonly known as THE BADASS ELEMENTbending (and known to Australians as THE BADARSE ELEMENT) is one of the four bending arts. THE BADASS ELEMENTbending is a sacred art to the Fire Nation and it allows them to control THE BADASS ELEMENT.
Firebending is the main element of Book 2: Fire, the last season of the original series.