And when you see someone standing up to bullies, don’t be idle, join them and stand in solidarity.
The Open Source Community Has No Place for Disrespect
Daniel Li

Every community (on github, that can be just one repo) has it’s own expectations of how to behave. Those expectations are shaped by everyone who participates there — especially the repo owner and regularly active developers.
Make sure you keep your own tone civil and focused on the issues, and yes, do try (when you feel able to) to point out poor behavior by others.
Remember: don’t make it about the individual. Make it about the behavior shown in a specific post.