My current workplace is already so surreally frightening with stupidity that I doubt anyone would notice a prank. Kind of a non-starter issue here.
Dredged from my distant past: As a grad student, I used to get assigned to give lectures to undergraduates. Some (usually the pre-meds) were so driven to ace the course that they would try to write down every word I said - everything - to memorize for the tests, and never look up. So I used to randomly insert nonsense phrases into my lecture to see how bizarre an utterance would be simply written down and memorized - and never even noticed as I said it.