Okay, as far as I know, they've never pinpointed the moment C&M became best friends, right? We can only assume it was when he moved in across the hall? That, or they were friends in college. The other night something strange happened to me, so I decided to base a fic on it.
It's before Mon goes to college. Ross is home, and Chandler is staying with his mother in Canada, m'kay?
Big thanks to Meggs for helping me out. The characters belong to me. Well, actually, they don't.
On with the fanfic.

The night was cold. Monica Geller lay wide awake in bed, her earphones on, playing music by Wham. Sleep just wouldn't come. Each time she'd closed her eyes they were pried open by some unknown force.
She hardly slept latley. She was never particully tired. It was okay. She'd just turn on the TV, with the volume down to the second lowest notch, so as to not wake up her family, and watch freaky gospel guys damning her to hell. There really should be more on TV at 1am.
Normally, she'd go upstairs to Ross's room and look out his window at the stars, but since he was home now, she couldn't. Monica had finished her last year of highschool, and this year she would join her brother at NYU.
Monica turned off her walkman. Listening to some guy saying "Wake me up before you go-go" wouldn't help anyone sleep.
That was when she heard the tapping. She couldn't figure what it was. She wasn't all in reality, and wasn't thinking straight. She ignored it.
Five minutes later, the tapping persisted. She started getting freaked. What was it? She sat up and turned to her window, which was behind the headboard of her bed. She could make out a dark figure. Someone was knocking on her window. "What the hell?" she whispered to herself.
She drew back the curtain, thinking this would reveal her night visitor. It didn't. The window was fogged up. She wiped the glass with her hand.
Chandler?
She saw her brother's college roomate. She got out of bed and undid the latch on her window. She opened it and looked out at him.
"Ross's window's the next one." she whispered in an annoyed tone.
Chandler gasped. "Shit!!" he whispered. It was almost a yell, but quiet as could be. "I thought this was Ross's window!"
"Well it's not." she whispered back.
"I am so sorry! Okay, um, go back to sleep. Sorry." he whispered pleadingly.
She sighed. "That's okay. I wasn't asleep."
"Oh. That's better then."
She laughed softly.
He laughed back. "Kay, I better go like, throw a rock at your dweeby brother's window."
"Okay."
He apologised again, and creeped over to below Ross's window.
She started to close the window, but realised something and stopped. She opened it.
"Psst! Chandler!"
Chandler was just about to try and wake up Ross when he heard her. He went back over.
"What?"
"Don't knock on the window. My parent's bedroom is right next to Ross's. If you wake them up, you're dead." Monica whispered.
"Oh. Thanks for the warning."
"Why are you here? Ross said you were visiting your mom in Canada?"
"I was."
"So why arn't you there?"
He grimaced. Then he whispered "She went to Europe with her new boyfriend promoting another one of her damn books. I was gonna stay there in Quebec, but I don't know anyone there."
"That still doesn't explain why you're here."
"I don't wanna go back to NYU, so I...kinda need somewhere to stay?"
"Ah."
"You think your parents would mind?" he asked hopefully.
"I don't think so. Here, come through the window and you can wake Ross up."
He smiled at her through the darkness. "Thanks."
He gripped onto the windowsill and tried to lift himself up. "Lil' help?"
She grabbed onto his arms and pulled him through. He fell onto the floor with a thud.
"Shit!" Monica whispered.
"Do you think anyone woke up?" he asked.
"No. Actually, you could go into my parent's room yelling and my dad wouldn't wake up."
He laughed. "Same with Ross."
"Speaking of whom, wanna go wake him up?"
"Alright. Where's his room again? I forgot, I havn't been here since last Thanksgiving..." his voice trailed off. They both thought back to then. Monica had accidently dropped a knife on his toe.
"Umm..." Monica broke the silence. "It's down the hall, past the kitchen, up the stairs, down the hall, and about the third door to your left."
"Eek. Sounds risky."
"You want to risk it? Because you could st...not." she'd started to say 'Because you could stay here.' but decided better of it.
"I think maybe I'll wait till morning. It might give me more of a chance of staying if I don't wake your folks up at quarter past one in the morning."
"Okay." she said. "Well, um, there's a guest room up the stairs, but again, that could be risky."
They were silent. Chandler spoke.
"Thanks."
"For what?"
"Just, y'know, helping me."
"No problem."
They were silent again as they glanced at each other uncomfortably, niether really knowing what to say next.
Chandler looked at Monica as the moonlight draped upon her face, she was so beautiful, he couldn't believe that he had once called her fat, he couldn't believe he had judged her right away like that and been so mean to say that, she was so sweet. He cleared his throat.
"Um, again, I'm sorry, for coming here in the middle of the night and everything."
"Oh, really, it's okay, I wasn't asleep."
"I still feel bad..."
"Don't. Really. In fact I'm glad you dropped by, I was bored, I couldn't sleep." Eventually the two started talking. They sat down on her bed and talked. About everything. She found he made her laugh, and vice-versa.
After making some crack about Ross, Chandler looked at her and smiled. Monica turned away from his look and remembered the whole toe incident. She had felt bad then - but now she knew him better and felt even worse.
She turned and looked at Chandler, she saw he was slightly looking at her but he quicky turned his head as he realized she'd been looking at him too.
Monica remebered how she'd had a crush on him and remembered exactly what she felt then as she was feeling now - they were the same feelings, but this one had more meaning, it was something deeper, more than just having a thing for him for his looks, she now knew just how nice and he wasn't insensitive as she had expected him to be. He was really great.
Outside, it was getting lighter. He checked his watch.
"Wow, it's 6:12."
"You're joking?"
"Nope."
"We've been talking since one."
"It seems like about half an hour."
"I know."
They looked at each other again.
"Actually, um, I think maybe I should sneak back out now and show up on your doorstep later on today."
She laughed. "Okay."
He got up and put one leg out the window, which was still open.
"I guess I'll see you later, then."
"Yeah."
"This can just be our little secret." he said.
"Sure."
"See ya."
Just as he was about to jump out, he stopped, looked up and kissed her on the cheek. "Bye."
Without another word spoken by either of them, he left.