See, that's when you start running.

[She giggles, enjoying the mental image of Joker fleeing from an angry shopkeeper while a furret wrapped around his neck sprays fire at the bushes entirely too much.]

Really though, as long as they're trained to use restraint with their attacks there's little to nothing to worry about, I'd say. He probably just doesn't really know how to control it, not being a fire-type and all.

Unless he's doing it on purpose. That's an entirely different problem.