Q: How do I stop Jira automatically setting me as a watcher every time I create or contribute to an issue?

A: In any Jira screen,

1] click your Account menu in the upper right-hand corner and choose “Personal Settings“:

2] In Personal Settings, change “Watch your issues” to “Disabled” and click the “Save changes” button:

that’s it!

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plucked from this Jira support page.