"Putting your foot in your mouth"

This is an idiom that means that someone said something without thinking and may have offended someone else who is present, without doing it intentionally.

For example:

Jim, Megan and Kara are in a room.

Jim says, "Hey Megan, what are we eating for dinner tonight?"

Megan replies, "I think we will have lasagna."

Jim, "Oh no! Not the same one that we had last week. That food was horrible!"

Kara says, "Awww, I made that lasagna!"