Oh sorry, I missed that. I think it wouldn't be out of place to ask him why he called after seeing the opponent already had a straight. However, without more evidence of chip dumping (e.g. history), it would be hard for me to give a penalty here. We don't really know if he misread A's hand, and then of course, B maybe thought he could still win (and he can by drawing a 5). This is something I see a lot with weaker players ("I had a pair, I couldn't fold...") In general, I agree with Tristan here.