Sentence:  In the '40s, I remember ludicrous puns thought to be funny and repeated by teenagers, sometimes to a chorus of laughter. Here is a <WSD>groaner</WSD> example: "Mother, get off the rafters. That is no way to get on the beam." Naturally, to understand the joke, it was necessary to know the idiom of the day. "Get on the beam" meant "get with it" or understand the situation. 
Meaning of the word marked with <WSD> tags:  A particularly egregious joke, especially a pun.