This is a tough one because it may well have happened more than once. But the one that first comes to my mind would be in "And The Answer Is" -- Clark has left Lois's apartment in mid-sentence ("Lois, I'm Super-- late for my appointment at the barber." <g>) after Jace Mazik calls, and when Clark comes into the office that morning, Lois is furiously typing some type of hate letter to Clark about his behavior. Jimmy says "you aren't going to say those things to CK, are you??" and then a moment later Clark comes up, asks Lois into the conference room, then cringes as he reads her screen and quickly deletes it.
Could that be the one you are thinking of? I have a feeling there are other cases.
Kathy
