put one's foot in it/one's mouth, to

put one's foot in one's mouth

 and put one's foot in it; stick one's foot in one's mouth
Fig. to say something that you regret; to say something stupid, insulting, or hurtful. When I told Ann that her hair was more beautiful than I had ever seen it, I really put my foot in my mouth. It was a wig. I put my foot in it by telling John's secret; he found out.
See also: foot, mouth, put
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

put (one's) foot in (one's) mouth

To make a tactless remark.
See also: foot, mouth, put
American Heritage® Dictionary of the English Language, Fifth Edition.

put one's foot in it/one's mouth, to

To make a (verbal) blunder. This term dates from the early eighteenth century and presumably was analogous to stepping where one should not. Jonathan Swift used it in Polite Conversation (1738), “The bishop has put his foot in it,” and a century later the term was defined in a book on slang (1823). Putting one’s foot in one’s mouth is of more recent provenance; it merited a definition in P. W. Joyce’s English As We Speak It (1910): “To a person who habitually uses unfortunate blundering expressions: ‘You never open your mouth but you put your foot in it.’” Today it is sometimes referred to as foot-in-mouth disease.
See also: foot, put
The Dictionary of Clichés by Christine Ammer
See also:
  • shoot oneself in the foot, to
  • a closed mouth gathers no feet
  • put one's foot down, to
  • foot up
  • bind up with (something)
  • bound up with
  • you put your foot in it
  • tag up
  • be hand and foot to (one)
  • on foot