I’m a SysAdmin since 1998. Maybe a bit earlier, if you count managing our home computer. This means SysAdmin Day is also celebrating me. However, my Emacs Calendar doesn’t show it for some reason.
The solution is pretty easy:
(add-to-list 'holiday-other-holidays '(holiday-float 7 5 -1 "SysAdmin Day") t)
Now invoke M-x holidays-list for any year, choosing “Other” as the category, and there you go:
… Friday, July 28, 2017: SysAdmin Day …