"Hey, hey!" said Eric*, sauntering into the park. "What up, my Smurfs?"
The tiny, blue folk collectively stopped what they were doing and gaped at him in shock. Brainy Smurf gasped. Weepy Smurf burst into tears.
"What?" Eric asked, "What, uh ... what is actually up? What's wrong?"
"You can't say that!" scolded Smurfette. "We can say that! You can't! You can't ever say that!"
"You don't have S-word privileges," Papa Smurf added firmly, though not without his characteristic gentleness.
"What?" said Eric. "I don't - I've said it before! I've said 'smurf' lots of times!"
"You've said smurf, and smurf," corrected Brainy Smurf, "And because you're a friend, we've even let you say Smurf."
"But if we're to remain friends," Papa continued, "you must never say Smurf."
Eric considered this. "You know what," he decided, "I think I'll be safe, and just stop saying 'smurf' altogether."
There was another round of gasps. Weakling Smurf fainted.
"I should hope so," grumbled Grumpy Smurf. "That's even worse."
* I am not familiar enough with any particular iteration of the Smurfs to give an accurate rendition of any of their canonical human acquaintances.