Isn't it plausible that Bos did indeed panic a bit because he got boxed in, felt he was slowly losing his balance and thought "Heck, if I'm going down because of you, I'm taking you with me!"? Who knows what kind of pressure Bos was under, and it was a very nervous finale with numerous crashes. For all we know, there could have already been little incidents in the previous kilometres. I believe there was mention of a crash at about 1,5 km before the finish, maybe Bos already got involved there somehow (maybe even barely managed to avoid it?), and got even more pumped with adrenaline? Which made him lose it when Impey boxed him in and he not only was in acute danger of crashing, but also saw every chance on a sprint victory vanish into thin air. In that case there's no real intention to take Impey down, but it could explain why he reacted the way he did, something along the lines of 'I just dodged a crash, no way I'm going down now and lose this sprint, you *******s'.