a remark or action that is a social mistake and not considered polite

I made a real gaffe - I called his new wife "Judy", which is the name of his ex-wife. 我一时口误出了大丑——把他的新任妻子叫成了“朱迪”，那可是他前妻的名字啊。

You started eating before anyone else had been served? What a gaffe! 没等其他人的饭菜上桌你就开始吃了，那是不是有点失礼啊？

Compare: slip noun