Never

Disclaimer: Disclaimed.

"Being grown up

Isn't half as fun as growing up.

These are the best days of our lives."

'In This Diary', the Ataris

"I WILL DEFEAT YOU, FILTHY HYOO-MUHN," shouted Zim. Dib didn't even look up, he knew Zim was on the ceiling. He cackled and jumped down. "AND NOW, FACE THE DIB... DIBBY... DOOM... THE MACHINE OF ULTIMATE DIB DESTRUCTION."

Dib rolled his eyes when Zim pointed the diamond shaped thing with spikes sticking up all over. Zim's smile didn't falter and he cleared his riffer-scisma loudly and obnoxiously before pressing what Dib assumed was a button.

"What the-" Zim hit it a couple more times. "GIR! WHAT DID YOU DO!"

"Uhh, nothing!" the robot in the green dog suit popped up behind Dib's chair. Dib sighed in time with Zim, causing Zim to glare at him.

"What is it, Dib-filth?" he asked loudly. "You aren't running away to warn all of humanity that I'm going to DESTROOOY YOOOU and then all of them."

Dib didn't respond. Zim's glare looked more like a half-squint right now.

"Dib?"

"Zim, do you ever get bored of this?" Dib asked. Zim raised an eyebrow.

"Huh?"

"Bored of trying to destroy me," he clarified. "It's been six years since we met and you still haven't taken over the world. Aren't you bored?"

Zim looked utterly confused. After a moment, the expression was gone.

"I SEE WHAT YOU'RE TRYING TO DO, DIB-STINK, AND IT'S NOT GOING TO-"

Dib got up and walked away.

"He-hey!" Zim followed. It occured to Dib just how short Zim was. He barely reached his chest. "I WAS TALKING TO YOU! HOW DARE YOU WALK AWAY FROM-"

"-the almighty Zim, yes, I know," Dib muttered. What would it take for Zim to realize he would never take over earth? By the looks of it, no other aliens seemed interested in the planet either. Dib was honestly a lot more worried about zombies at this point than aliens whose own leaders didn't even take them seriously.

Zim stopped moving, scrutinizing him.

"Is the Dib feeling okay?"

"I'm fine, Zim!" he said, frustrated. "Everyone is! At least, from you."

Zim gasped dramatically. "You laid out a trap!"

"No, Zim," he said.

GIR hugged Dib's leg. "I wanna tickle you!"

Dib ignored him. "Zim, seriously, I'm sick of your little game. Why don't you just grow up?"

Zim couldn't mature then if he wanted to. The Irken grew at a much slower rate than humans. Dib knew that, he just didn't care anymore.

The alien's expression then was pitiful.

"You're serious?"

"Yes!"

"...does that mean I win?" Zim said gleefully.

"No," Dib said. "But if you want to think that, I don't even care anymore."

"But..." Zim said.

"What, Zim?" Dib exclaimed. "What could you possibly want?"

"But I still want to destroy you..."

Dib didn't say anything.

"DIB!"

"WHAT?"

"Remember the time when you went to study real science?"

Dib winced. Yes.

"Aaaaaaaaand it was horrible because you had a duty to save humanity?"

"That was back when I thought you were a threat."

Zim had heard enough. He ran over to Dib and latched onto his head, chewing on his ear.

"ZIM, GET OFF!" he screamed and stumbled around. "WHAT IS WRONG WITH YOU?"

"YOUR MIND HAS BEEN REPLACED WITH KETCHUP!"

"ARGH!" he couldn't see and fell onto the table.

Gaz chose that moment to walk in.

She didn't say anything or even roll her eyes, just kept pressing buttons on the GameSlave4.

"ZIM! I'm serious!" He ripped Zim off his head, crying out as he tore some of his hair with it.

Zim fell on his back and jumped up, cackling. "VICTORY FOR ZIM!" he held up the chunk of Dib's hair.

"Ok, can you get out now?"

"OH YOU WISH I-"

"Yes. I do."

...

It was a long silence and Dib felt somewhat bad. He just didn't get why Zim wasn't sick of this nonsense after six years of fighting.

"...fine, Dib-worm," muttered Zim. "BUT I'LL BE BACK, YOU WILL SEE!"

He laughed loudly and maniacally. A laugh Dib was extremely familiar with. Annoying as that was.

"Yeah, sure, whatever."

And he was back. He was back twelve times before he finally got it.

Zim never grew up.

Not while Dib was alive, anyway.