Let me first sincerely apologise for what may seem like a frivolous question here!
However, as I'm fortunate to work in an organisation and team that has a sense of humour and where "prank of the week" is almost a tradition, I thought I'd add in with a most horrid one:
The font in JIRA tickets - at least in the description field - shall be Comics Sans for a day!
Is that possible in such a way that it can also be undone (at least moving forward, even if tickets of that day remain in CS)? This would specifically be for tickets that are auto-generated through a variety of batch and monitoring systems, so not necessarily hand-entered ones.
I'd threatened folks with this before and mostly got a "we dare you!" back...