I'm not sure it counts since he was being influenced, but the angriest I recall is when he says, "Don't you tell me what to do!" to Riker in the episode with the mindmeld with Sarek. The tone of his voice was pretty intense and I think that's the only time he's actually went full-tilt-boogie and lost his cool completely. Though, as noted, he was being influenced and that was the only thing that lead him to that point. But I remember when I saw that episode I jumped alittle when he yelled like that and was like, "Damn" pretty much just like Data in that scene.
