Once had a user manually change their ticket to Priority 1, which we used to indicate dozens of people/everyone down, because their M key only worked half the time they pressed it.
We don't have a priority system, but users take it upon themselves to add things like 911, URGENT, and ASTAT in the title. It's kinda fun, you can tell what rumor had been flying around the office when every ticket suddenly has the same "priority".