Children will always be children. Yes, that includes Kakashi because he's as childish as they are.
Also, Iruka is doing an intervention but no one even notices it.
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"Can I ask you a question, Iruka?"
"Sure. What is it, Kakashi-san?"
"Why are my three greml- I mean genins doing here in your house at this time of night?" he pointed at the three said genins sitting at the table, hunched over a strip of paper as they write on it.
"It's rude to point, Kakashi-san." Iruka admonished him lightly. "And why not? They expressed an interest on learning how to make seals so I thought, "why not?" and brought them here." he explained.
"Right, let me rephrase that question. Why are my students asking for your help instead of me? I'm the one who had learned seals from the Yondaime himself. Doesn't that mean that I'm the most qualified to teach seals?"
"Between you and I, which of us use seals more?" Iruka calmly asked.
"...you."
"And which of us has more knowledge and understanding about seals that could par with the great Toad Sage himself?"
"...you."
"And whom, between the two of us, does Sandaime actually listens to?"
"Well actually-"
Iruka stared him down until Kakashi slightly deflates.
"...you."
Kakashi glared at the genins when the snickering starts. Silently, he signed in Anbu code that said he will definitely get back to them if they don't stop.
The three genins feigned confusion despite the fact that they know that he knows they know Anbu code. He did teach it to them after all.
"Stop threatening them, Kakashi-san." Iruka said without looking up from his work.
"You know Anbu codes?" Kakashi blinked in surprise at Iruka.
Now it's Iruka's turn to blink in surprise. "You taught them Anbu codes? In five days?" he asked, baffled. "And I don't need to understand it to know you're making threats."
"They picked up quick." Kakashi shrugged.
Iruka turned to look at the genins. "You learned Anbu codes in five days?" he asked them.
"It's easy to remember," Sakura replied.
"I already knew some," Sasuke told.
"I already knew," Naruto said.
Everyone on the table stared at Naruto. Naruto stared back.
"How?" Kakashi asked.
"I broke into Anbu's headquarters once and saw a book about Anbu codes. They had a lot from what I see so I 'borrowed' one and never gave it back." Naruto shrugged like it's no big deal.
"Wait, hold up, you broke into Anbu headquarters and didn't get caught? How?" Sakura looked at him in awe and disbelief.
"Fox luck," Naruto answered as he pointed at his Fox mask. "Thanks to this, I can get into almost anywhere!"
"Anywhere?" Sasuke asked.
"Anywhere!" Naruto chirped.
"Anywhere?" Sakura questioned.
"Anywhere!" Naruto affirmed.
"Anywhere?" Kakashi slides in.
"Any-"
"Alright, we get it. Naruto can get into almost anywhere." Iruka interrupted. "Now get back to your seals. I want it done today." When Kakashi made a move to say something, Iruka glared at him. "Don't even think about doing that again or I will use my seals on you," Iruka threatened.
The four of them immediately settled down but throughout the night, grins and sign language were exchanged and they all giggled like school children at their inside joke, much to Iruka's exasperation.