The first week or so, he used it appropriately:
"Isaak, would you like more milk?" "No!"
"Isaak, can I have your airplane?" "No!"
"Isaak, do you want to wear this shirt?" "No!"
Then, earlier this week, he tried something new. I smelled a suspicious odor, and asked him, as I always have, "Isaak, are you stinky?" (OK, I used a different word, but my father is reading this...) Isaak looked directly at me and shouted, "No!" Hm. Well, we both knew the answer was NOT "No", so we had another round.
"Isaak, when Mommy asks you if you are stinky when you ARE, and you tell Mommy "No!", that is called lying, and you will get your bottom spanked. Let's try again. Isaak, look at Mommy's eyes. Isaak, are you stinky?" Isaak looked away and shouted, "No!" I gave his diaper a token swat. He responded with token tears. Briefly. And asked for a hug.
Then we tried again. "Isaak, look at Mommy's eyes." He looked at the floor. "Isaak, look at Mommy's nose." He looked up at me. "Isaak, are you stinky?" Again he shouted, "No!" I asked, "Are you lying to Mommy?" Isaak nodded his head and said, "Uh huh." Hm. Well, we were getting somewhere, anyway! After a little firmer of a swat, a little bit more sincere tears, and another hug, we tried one more time.
"Isaak, are you stinky?" Isaak nodded.
And he hasn't used the word "No!" inappropriately since.