Who are the decision makers of what needs to be in the Code of Conduct?
Site owners? Moderators? Voters?
For example, I would strongly oppose the guideline "Avoid sarcasm". Is there a way to influence the Code of Conduct in that direction?
The Code of Conduct is made by the site owners and applies to all sites in the network (it's just hosted in different places). It has seen a couple of iterations so far, and they do request feedback from the community on Meta Stack Exchange:
Sarcasm can be a great tool when properly used. The main problem, especially in written form, is that it's often hard to distinguish from unfriendly language or worse. For many users here (including me) English is not their first language, and being from different cultures may influence people's understanding of or reaction to sarcasm. Therefore, the Code of Conduct advises against using it.