实锤 + perfective 了 - 'solid proof has landed'. Used for gossip scandals (affairs, plagiarism, cheating) when screenshots or video surface. 了 marks the moment the truth gets nailed down.
culture
Born on Chinese entertainment Weibo around 2014. The image is a blacksmith's hammer (锤) striking something solid (实) - you've pounded the case shut. Twitter equivalent: 'got the receipts'.
