Years ago when my kids where much younger, I was quizing my son about something. After he had answered, my daughter snapped at him, "Don't lie!"
"Dad lies," he answered defensively.
Somewhat taken aback, I asked, "When did I lie?"
Then he quoted some ridiculous thing I had said about somebody a short time ago.
"I was teasing, not lying," I explained.
"What's the difference?" he demanded.
I knew I had to think quick, so I said, "It's called the 2-second rule."
"What's the 2-second rule?" he asked. His question gave me just enough time to make something up.
"The 2-second rule is: if something cannot possibly be believed for more than 2-seconds, it doesn't count as a lie."
A couple of years later, the 2-second rule came in handy. My son had "fallen in with the wrong crowd," and was in trouble with the law. It seems one of his "friends" had stolen some other kid's boom-box, and when the crime began to unravel, the friend talked my son into hiding the "hot property" in our yard. Kids were buzzing about the house. At one point, before I had figured out what had happened, my son burst into the house, obviously in a highly agitated state.
"What's going on?" I asked.
"LIAR!" my daughter shot back.
I took a deep breath, then said in that calming, TV-dad tone, "Well technically--under the 2-second rule--it's not a lie."
I can't say we all had a good laugh, but it certainly broke the tension, because we all knew his "nothing" answer couldn't possibly be believed for even 1/4 of a second.
The truth was shortly forthcoming.