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A person monopolizing a bathroom, (especially, but not necessarily, at work) is said to be celebrating his or her Diamond Jubilee. In other words, the individual has been on the throne way too long.
"Ugh, what's with the long line? I need to use the bathroom!"
"Joe had Mexican for lunch. Now he's celebrating his Diamond Jubilee."
by Mr. Me, Esq. June 29, 2012