短语 to flex one's muscles 的字面意思是“活动肌肉”，人们借用这个形象的画面来描述一个人或机构对他人“显示实力，展示力量”。

例句

Our boss spent a lot of time flexing her muscles at the meeting this morning. She wants us to know she's in charge.

在晨会上，我们的老板花了很长时间向我们展示她的实力。这么做是为了让我们知道在这里她说了算。

Don't pay any attention to Steve. He just likes to flex his muscles around new people but he's a very sweet and gentle guy, really.

不用把史蒂夫的举动太放在心上，他就是喜欢向新来的人展示自己的能力，其实他是个非常和善温柔的人。

I thought you were a bully when we first met, but now I know you I realise you were just flexing your muscles.

咱俩刚认识的时候我觉得你就会欺负人，但现在我明白了当初你也就是在展示自己的能力。