When you say something, as a result of thoughtlessness, and caused an awkward situation, say making someone feel embarrassed, you have put your foot in your mouth.

• 由于无心而说错了话；导致了一些尴尬或者引起了一些麻烦.；那种情形下你都可以说你是"把自己的脚放到自己的嘴里了"