First, it's two sentences, although periods are omitted.
>
> Kyoto people don't say "Die!" (to someone). (Instead,) They say "Oh this person is dead" after killing them.
I think you can get the main part of this joke from the translation. Basically this is an ethnic joke that is making fun of the cold and sarcastic trait of Kyoto people. is a Kyoto-ben version of . (This tweet also shows the stereotyped image of Kyoto people. Well, who said sarcasm doesn't exist in Japan?)
In addition, by itself sounds funny. This (or , ) is a stereotyped feminine (or "geisha-ish") Kyoto-ben variant of . Naturally, it comes after a noun or an adjective, but not after an imperative form. A "correct" Kyoto-ben sentence for "Die!" would be something like . Therefore, this tweet initially looks like a serious Kyoto-ben lesson, but it turns out to be a dirty joke in the second sentence, which makes the tweet even funnier.