“忘恩负义的”常见的英文表达是 ungrateful ，读音：英 [ʌnˈɡreɪtfʊl]；美 [ʌnˈɡreɪtfəl] 。
例句：
It's ungrateful of you to forget all the help he gave you. 你忘记他给你的所有帮助，真是太忘恩负义了。
He was accused of being an ungrateful son who abandoned his elderly parents. 他被指责为一个抛弃年迈父母的忘恩负义的儿子。
此外，thankless 也有类似含义，侧重于指做了某事却得不到感激，也可表示“忘恩负义的；吃力不讨好的” ，读音：英 [ˈθæŋkləs]；美 [ˈθæŋkləs] 。
例句：
He felt like a thankless fool for all his efforts. 他觉得自己所有的努力都白费了，像个忘恩负义的傻瓜。