It's even [listed in the faq][1] and everything:

> ## Etiquette
>
> Civility is required at all times; rudeness will not be tolerated.
>
> ### Be nice.
>
> Treat others with the same respect you’d want them to treat you. We’re all here to learn together. Be tolerant of others who may not know everything you know. Bring your sense of humor.




[1]: https://serverfault.com/faq#etiquette