Bakana is Japanese for impossible or also used to highlight the ridiculousness of a situation. Bakana is frequently used in Anime and Manga.
Villain: Launches "sure to kill technique".
Hero: Dust Clears and hero is still standing. Usually makes snarky comment "that all ya got"
Villain: Bakana how are you still alive.
It comes from the two words "Baka" and "deredere". Baka and deredere is in Japanese. Baka means idiot and deredere means "lovey dovey". So bakadere basically a clumsy and idiotic person, who also is sweet and kind
Bakadere is mostly used by people who watch anime, or read manga