An exclamatory statement that is meant to pass blame from one party to another; the party that issues the statement invariably is "in the wrong," as the misinformation is always caused by that party either not paying attention to what was actually said or subconsciously distorting what was said into what they wanted to hear.
Learner: "Butchused(!) we weren't having the test!"
Instructor: "No... I said we weren't having the test this week. It was pushed to Monday."
Father: "Ok kids, lets hop in the car and head home."
Child: "Butchused(!) we would go get ice cream!"
Father: "I said we would get ice cream if everyone finished their chores. You didn't do any of them."