A pyro: One who is a pyromaniac, and thus not at all adverse to using fire and sometimes the occasional literal flame to get things their way, or just burning things down because it is shiny.
The PPC, despite being largely headed by sentient Flowers, has a lot of these, as well as enough flamethrowers around to make instances of mad agents going flamethrower-crazy a not-uncommon occurrence. Fortunately, there's a whole department where their tendencies can be put to good use. If someone refers to "a Pyro" in Headquarters, chances are they are referring to an agent in that department.