Put One's Foot In It Meaning

(idiomatic) To make a mistake in public, or a social blunder, that is embarrassing, or offensive.

Example: 1968, The Heart Is a Lonely Hunter, 00:20:20:
  "It's time i was getting dressed for a party." -- "Whose party?" -- "Mary's.. (awkward silence). Oh, I guess I put my foot in it. I just took it for granted you'd be there." -- "She didn't ask me." -- "I could just bite my tongue".