if he can, how long? im asking this cuz if he needs to breathe , i can actually declare a weakness of one punch man..

@worldbreakerhulk: It was shown that he had to hold his breath for a bit in episode 12. So maybe he can't.

even his weakness is a gag

He said that humans can't fly, so I would assume thet he breathes like the rest of us.

No. He may have enhanced lung capacity (enabling him to hold his breath long in a thin atmosphere or vacuum) but sooner or later he needs to breath.

Their is this one idiot who remarked that Saitama can not die from the lack of air (not tacking into account that his last major fight to place in an environment with thin atmosphere).

https://comicvine.gamespot.com/forums/battles-7/pre-crisis-black-adam-and-shazam-vs-saitama-and-ga-2274597/?page=1#js-message-26774667