(informal) nenamáhat se, neunavovat se, šetřit s dechem (marnými radami atd.)
No one is listening to your advice, so you might just as well save your breath. (English Idioms, Oxford)
I don't know why I bother speaking to him - I might as well save my breath.(CALD)
I don't know why I bother talking to you -- I might as well save my breath. (CDAE)
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