Are School students are taught that lying is a sin?

School students are taught that lying is a sin. However, instructions also advised that using a bit of imagination was OK to express the truth differently without lying. Below is a perfect example of those teachings:

Getting a Hairdryer Through Customs:

An attractive young woman on a flight from Ireland asked the priest beside her, “Father, may I ask a favor?”

“Of course child. What may I do for you?”
“Well, I bought my mother an expensive hair dryer for her birthday. It is unopened but well over the Customs limits and I’m afraid they’ll confiscate it. Is there any way you could carry it through customs for me? Hide it under your Robes perhaps?”
“I would love to help you, dear, but I must warn you, I will not lie.”
“With your honest face, Father, no one will question you,” she replied.
When they got to Customs, she let the priest go first. The official asked, “Father, do you have anything to declare?”
“From the top of my head down to my waist I have nothing to declare.”
The official thought this answer strange, so asked, “And what do you have to declare from your waist to the floor?”
Father replied, “I have a marvelous instrument designed to be used on a woman, which is, to date, unused.”
Roaring with laughter, the official said, “Go ahead, Father. Next please!”