From the xmasprompts list on tumblr (it's the name of the blog)
I was beautifully given a reason to write fluff Mondler, so there you are ;) And happy new year! (this has nothing to do with it, but still)
Day 16: Kiss
The first time Monica kissed Chandler was after that disastrous Thanksgiving. She came to see him, alone, and although she had just cut his toe, he couldn't help but feel attracted by this strong, beautiful woman. His mother - and father, unfortunately - had whined enough to him about how hard it was to lose two pounds, so he guessed that losing so much weight in a year required a strong will. And Monica looked absolutely beautiful.
She apologized, looking away, but he dismissed it - or something like that, he was pretty high on medicine. Then they talked shortly and she left, kissing his cheek before running away. He stared at the door and touched his cheek, cursing his brain to have a crush on someone who had just cut his toe.
They didn't kiss for a long time. Not until Monica was depressed about her mother not even congratulating her for succeeding her culinary school. Chandler made a show of himself for her. He applauded too loudly, he yelled her name, he screamed he was proud. Everyone around was looking at him weirdly or amused, but he didn't care. His friend was feeling bad, and it was his duty to make her feel good. Even Ross told him to keep it quiet. He ignored him - he didn't know how lucky he was to have a sister like Monica, or how lonely he would have been without her. Monica's smile was all Chandler needed and when he saw her running to them, looking happy, he couldn't have been prouder. Later, when they were alone, she thanked him and talked a bit more about how her mother had really always been like this. He listened and smoothed her back until she fell asleep, exhausted - and a bit drunk, he was sure. He kissed her forehead without thinking, and put his own jacket on her body.
They picked up the habit of kissing each other's forehead along the way of becoming best friends. Or realizing they were best friends, really. He would always kiss her forehead when she felt bad and she would always smile and hug him if she could. She kissed her forehead too, but then moved to his cheek while he kissed her hair. It was always friendly, Chandler never thinking once of more - or maybe after a break-up but that was his fucked up mind thinking.
He was the one to kiss her on the lips first. It wasn't a first romantic, beautiful kiss. It was a drunk, clumsy kiss, and he was honestly surprised it hadn't happened sooner. He didn't remember much of the party, but he remembered the kiss. She was as beautiful as ever, and he was drunk and near her, so it somehow happened. He put his arm around her, mumbled she was gorgeous, and kissed her. He remembered it because she responded eagerly and he thought that for once it was going well. Well, until Ross and Chandler's date for the evening saw them and pulled them apart, that is. Chandler pretended he had kissed the wrong chick, while Monica simply didn't answer anything - usually a proof of how drunk she was. The kiss had been amazing, but Chandler never said so. He pretended to forget, and he never knew whether Monica remembered.
They kissed more after. Often when one was drunk, or sometimes just a friendly kiss. The first time they were sober was because Monica was quickly saying goodbyes before having to leave for Christmas. She kissed Phoebe on the mouth and Chandler was next to her so she kissed him automatically. It was entirely platonic, and Chandler didn't enjoy it romantically, but he still was happy. It happened more than once afterwards.
Chandler's crush on Monica died out for a long time. Or at least it was small enough for him to pretend he didn't have one. It came back strongly at some point, for no reason. Maybe he was getting older, more mature, and he was wondering about his love life. Sometimes, he thought she would be the only woman he would be able to deal with on a daily basis. He didn't see himself dating a Janice his whole life, and the only girl he was comfortable enough with was Monica. So he didn't know whether he had a crush on Monica or on the life he imagined with someone like Monica. It was weird. But he kissed her hair a bit more and his hand lingered a bit more, and he hugged her a bit more. Nobody noticed, except maybe Monica herself, but she didn't say anything.
His crush stopped after the trip to the beach, or maybe when he started dating Kathy. Or maybe after the break-up, when he decided that a divine entity had cursed him never to find love. He tried to stop falling in love. He had crushes on some girls, but he tried not to suffer from it. That was until Monica was the one to kiss him. A bit drunk, yeah, but not at all platonic. His crush came back full strength on, and he wasn't sure he could repress it anymore, especially not after having sex with Monica. He tried to, because they were best friends, but he wanted to date her so badly. He gave in, and his crush never left, or only to turn into love.
He still kissed her cheek and her hair and forehead, but he also could kiss her lips and her neck, and her ear, and her shoulder, and any part of her body he wanted. He loved to kiss her for anything, really.