Wash isn't exactly looking for a fight -- it's probably in his best interests to avoid one, not when he only has a vague idea of Tarn's capability. From what he knows he's fairly confident he can take him, but Tarn is armed, and the last time Wash had taken a chance it hadn't worked out so well. Less trying to provoke, more trying to prod and dig and learn more about this person he's only heard about through others -- and trying to gauge why he's here. If he should be worried, if he's an immediate threat.

"Try me. I'm a great listener." He actually is. "And I'd really like to know what you think you're doing out here."