Exaggerated: Patrick is completely Ax-Crazy and tries to burn down everything around him, constantly.
Patrick suffers from low-level pyromania and satisfies himself by burning junk mail, dry grass and other harmless actions in the safety of his own home.
Patrick has a more realistically-portrayed form of pyromania, and merely carries around a lighter that he flicks on as a release whenever he's feeling stressed. Otherwise, it doesn't cause many problems.
Justified: Patrick is diagnosed with actual Pyromania.
Patrick has Pyrophobia: The mere presence of fire makes him flee, turn catatonic, or suffer other forms of mental breakdown.
Pops Sickle is a cyromaniac, and his unnatural fondness for the frigid has gone past the point of eccentric and turned him into a stone cold killer who derives sadistic glee from watching the warmth slowly leave his victims' bodies as they fall into the cold embrace of death.
Patrick has an unhealthy obsession with water.
Although Patrick inevitably seems like a pyromaniac, it turns out he's actually a professional and uses fire because it's an effective weapon instead of any personal love of it.
Alternatively, it's not setting things on fire in-and-of itself that Patrick enjoys. It's the hurting and killing people part that makes him happy.
Double Subverted: ...But he's only professional at work. At home he routinely starts fires to amuse and comfort himself.
Patrick's entire vocabulary is related to fire. He constantly goes around giggling about how much he loves fire.
Patrick is infamous for incinerating / blowing up something all the time, even when it would be implausible (ie: such as water, fire-retardants, etc.)
"You know, sometimes I wish people wouldn't mistake me. Yes, I can fire fireballs from my hands. Yes, I was born with this power. No, it does not mean I'm about to start giggling over starting fires with them."
Patrick seeks help to overcome his pyromania.
Discussed: Two characters are looking at Patrick at work and comment upon how he seems to enjoy it, and the possibility that he might suffer from Pyromania.
Conversed: Two characters watching a show on superheroes comment on how often villains with fire-based superpowers seem to combo it with genuine pyromania, and how this almost always is of the 'burn the world down' level unlike gradual onset like with most Real Life insanities.
Patrick is genuinely insane and suffers from lots of personal problems that he represses through starting fires, knows he has a problem, and routinely goes to therapy to stop himself from burning and hurting people just because of his compulsion.
Alternatively; because Patrick burns things to relieve stress, he ends up causing even more problems, resulting in a endless cycle of problems and setting things on fire.