To re-establish your classy credentials, circle back to the more positive aspects of your last experience. "Try to immediately turn it into something positive," she says, adding, "Always talk about what you learned from the experience. If possible, be complimentary to your former employer and colleagues."
Post-interview cleanup. As Oliver points out, the interview is only one part of a longer "campaign" to getting hired by a company. If you failed to apologize or feel that your already-uttered apology wasn't enough to erase the negative impression you left, address the matter once more in your follow-up email. "When you're thanking him or her for the meeting, you say, 'I was thinking a little bit more about the question that you asked and I wanted to provide further clarification,' and then fill in the answer you should have given on the spot," she says.