"So, do you understand why I sent you out of the room?"
"It's NOT FAIR! I didn't say 'Ewww!' I said, "Oooohhh!'"
His eyes are full of tears at the monumental injustice of this situation.
"Boris, I was standing right there; I heard you. The reason I make such a big deal about this is..."
"But it's NOT FAIR!!"
I break out the Stern Teacher Glare of Doom . Boris stops protesting and makes a lateral move to seething, sniffling resentment.
"As I was saying, the reason I make such a big deal about the whole 'Eww...' thing is that everyone around you is taking a big risk by trying something new and when you make fun of the food, it makes it harder for them to take a risk."
"But I DIDN'T!! I was just..."
"Boris, I'm going to interrupt you here. I'm not mad and you're not in trouble. My homeroom students are waiting to get into the room. I just want to make sure we understand each other."
"Do you want to argue with me or do you want a piece of candy?"
It's a tough choice, but after a second or two, he goes with the Turkish Delight.