The 'c' to create a Jira issue shortcut. I personally hate how it can be triggered in the weirdest places, where I would almost never create an issue (like setting a field context with an issue type and a project that both have the letter c in them). I know keyboard shortcuts can be disabled per user, but it's only that particular shortcut that grinds my gears.
What's your Jira/Confluence pet peeve?