not contacting the author if you have a bug fix or improvement to their extension
not answering to a patch to one of your extensions that you received
writing bad non-informative bug reports with no way to reproduce them
not providing a better bug fix once the first one has been rejected
rejecting bug fixes or improvements for no good reason
forking an actively maintained plugin
releasing insecure code
re-releasing someone else's extension without contacting him first, not letting the original author intercept this act, thus putting users that use this extension for everyday work and try to upgrade at a risk.
Good behaviour is:
accept responsibility for the code you once contributed
take over responsibility for code that has been abandoned
take care that nobody messes up our code
try to collaborate with the original authors
accept additional features "with taste"
comment on added features and give people a chance to come back with an improved patch
be thankful for any bug that someone reports
be even more thankful for any bug that someone fixes
have deep respect for people opening up a can of worms
be able to communicate about bugs and code and whatever
be open-minded and able to accept that you were wrong in your bug report and a short RTFM answer
be able to accept that the code or patch you provided is indeed totally crap
be able to say one of the following sentences occasionally:
Oh, I see now.
I was wrong.
You are right.
I don't know.
Can't we do both?
Shit, what was I on when I wrote this code?
Wow, what a great idea!
accept that the original author is the official authority for his/her code
be eager and willing to learn, either by yourself or by listening to more experienced people
be able to put aside your own ego and still remain authentic
take everything with a dash of humor
have a certain acceptance for people not behaving well
take care that the project is not put at risk by bad behaviour, or accepting too much bad behaviour