To spit at the sky only to have the spittle fall on one's own face; to try to harm others but end up harming oneself; to shoot oneself in the foot; to hoist with one's own petard.
他总是在背后说别人坏话，以为没人知道，没想到最后事情败露，真是仰面唾天，自食恶果。
He always spoke ill of others behind their backs, thinking no one would know, but in the end, the truth came out. It's truly a case of spitting at the sky and having the spittle fall on his own face, suffering the consequences of his own actions.
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