Set during the time Cas is human
It was a Thursday when Cas realised that he had a preference. He didn't really understand why, he just knew that he did. On the next day, Friday, he called work and said he had a family emergency, and he sat Dean and Sam down in the bunker to tell them. When Sam heard, he laughed, and threw his hands into the air before walking from the room. Dean put his face in his hands, shaking with laughter. It had been a while since Castiel had seen Dean laughing. Dean gave Cas his congratulations, and left as well. Cas was confused. He thought things like this were important? Being a human was hard. When he asked Sam why they had reacted that way, Sam told him it was because it was more then a little obvious. Cas supposed it might be, considering he always openly preferred it. Later, Dean came to him, and asked Castiel if he wanted a pb&j sandwich for dinner. Cas smiled and nodded vigorously. Dean laughed. The next day, Saturday, Castiel went back to work. When his manager at the Gas n' Sip asked what had happened, Cas explained that he had to tell Sam and Dean about his decision. His manager look at him incredulously, and asked if he was serious. When Castiel said yes with a perfectly straight face, he was fired on the spot. Castiel was sad. He had liked that job. When he told Dean and Sam about what happened, they laughed some more. Cas thought that was a bit cruel, but when they promised to help him find a job, he forgave them. Castiel was still confused as to why every seemed to think this was still some big joke. He was sure that it was a big deal hin the human world. He was not very sure. He did not know why it was such a big deal. When he asked Sam, he laughed and said it wasn't. When Cas told Sam that Dean told him that preferences were a big deal, Sam laughed, looking at Castiel with an amused look.
"Dean meant your sexuality Cas! Not grape jelly over strawberry!"
Yay! Cute little Human!Cas story for you.