The phrase is everyday spoken German, with esst lieber mal nen Apfel meaning you would do better to eat an apple. No confirmed film, show or creator source is attached to this recording, so it circulates mainly as a short reaction clip on soundboards and in chats. Its humour comes from ordinary, sensible advice being used out of context, which is why German-speaking users share it around food, dieting and snack choices, often alongside other short German meme lines like kann es sein das du dumm bist.