Huh? I said Sasuke wasn't going to kill Deidara, he wasn't a threat to him at all considering it was said they both were out of chakra.
i know what you said, but you're looking at it the wrong way. In the moments leading up to the start of that fight, Deidara wanted to do everything in his power to kill Sasuke from jump just because he allegedly killed Orochimaru and he makes it pretty clear that he was the one who wanted to do it. It didn't matter if Sasuke was out to kill Deidara or not, seeing as though Deidara had every intention of killing him on that basis alone.
Seeing as though everything else was countered by Sasuke's use of Raiton, it was the one move up his sleeve that he though Sasuke wasn't able to counter with that. It only appears dumb because it turns out Sasuke was prepared for a situation of that nature, but Deidara couldn't have possibly known that. Hindsight is always 20/20.
