I don't know why on earth Jotaro would actually kill a guard dog but being that he is SO MUCH like Musashi (well Takezo) it really is a shame that he didn't think how reckless he was being with the dog in the first place.
And also Musashi is pissing me off because he was truly starting to get along with real samurai and he just HAS to ruin it by being his arrogant self :(