In the order that I recall then:
The delightful Australianism Nicko: only once from a blokey geography teacher.
Acka Nicka in my local high school (where I mercifully only stayed a year), because of my premature acne.
Nick Squared in my elective high school, because Nick Nicholas.
NSN as an undergraduate, because I used to use my patronymic as a middle name, so that was the email address I was allocated.
The Minoan Genius in postgrad by a fellow historical linguist, because we came across the phrase once in some crackpot Basque interpretation of the Phaistos disc, and I’m from Crete.
Not nicknames as such, but I appreciate it when Greeks call me Nikóla or Nikolí, which are familiar forms of Nick. Conversely, I resent the hell out of it when they call me Nik. Am I speaking in English to you? No? Then it’s Nikos. Damnit.
I nickname people obsessively here, but I don’t think I’ve gotten one in return. Be careful what you wish for, I guess…
EDIT: Philip Newton reminds me of opoudjis, on which see Nick Nicholas’ answer to How did you get your nickname? I don’t even think of that as a nickname, but that is how it got started.