I would think when if you've lived 200+ years and can summon giant evil demons and order around super talented ninja criminals you should be able to act however the heck you want.

Besides, it's not like there isn't a precedent, Jraiya acted like an idiot ladies man all the time and he was one of the strongest ninja in the Narutoverse and Kakkashi reads a hentai novel in his spare time. Being a badass ninja doesn't mean you have to be serious all the time, in fact the mor badass a ninja is the less need to be serious all the time.