Your story of starting to say something and then chickening out, reminded me of this one.
Back when my son was about 4 years old (he's now 15) I was out driving with him. We were stopped at a stoplight, and for some reason, I thought the light had turned green, but it hadn't. I started forward. I immediately realized my mistake, said "Oh, shit!" and slammed on the brakes. No harm was done--I had only moved a few feet--but I felt embarrassed about having used a "bad" word in front of my son. I didn't want to set a bad example for him. So I figured I shouldn't let the incident pass without comment.
So I gathered my courage, as we proceeded to drive home, and I finally said, "You know, I said a bad word back there."
"You did? What was it?"
"Oh, well, if you didn't hear it, then I guess it doesn't matter. Never mind."
"No, tell me! What did you say?"
"Well, I really don't think I should repeat it."
"No, tell me! I want to know!"
"No, I'm not going to repeat it."
"Did you say STUPID?"
Maybe a word of explanation is necessary here. He had been taught, in day care apparently, that it's not nice to call other kids stupid. So he was left with the impression that "stupid" was a dirty word. Not wanting to explain the difference between "stupid" and a REAL dirty word, I had decided to leave well enough alone. But at this point in the conversation, I had to smile.
"No, I didn't say STUPID."
"What did you say then?"
"I told you, I don't want to repeat it. So just forget it."
"Did you say FUCKER?"
At this point, it was all I could do to keep from running off the road! "Willie! I didn't know you knew that word!"
"I know tons of 'em. I hear 'em all the time in day care."
It took me a minute to recover from the shock. "Oh, well, then, I guess I might as well tell you. The word I said was SHIT."