cry in one's beer 的意思是对着自己的啤酒哭，也就是顾影自怜，自我怜悯，借酒消愁。

【例句】
John sits around in a bar all day crying in his beer since his girlfriend dumped him.
自从John的女友和他分手后，他就一天到晚坐在酒吧里借酒消愁。

Instead of sitting around in a bar all day crying in your beer about not having any money, why not get off your bottom and go out and look for a job!
与其成天坐在酒吧里，因为没有钱而可怜自己，你为什么不振作起来到外面去找个工作呢！