The same guy who was also described as being no "boy scout". So he's seems to have made different impressions on people.Was it Kirk who called himself a "Stack of Book with Legs"? I could swear it was Gary Mitchell?
It was Mitchell. Kirk describes himself as "positively grim" in "Shore Leave" when talking about Finnegan. But he was probably a Freshman at that point and I'm sure some things changed as he grew comfortable with his surroundings.
He was at least no boy scout when it came to the ladies. We met a number of women from his past in TOS and heard of one he almost married. That doesn't have to mean he wasn't a straight arrow when it came to academy work. So it really isn't contradictory information or behavior.
I think something about the K-M test affected TOS Kirk in a more profound way than it did nuKirk. Maybe the experience bothered him because it made him begin to realize there were flaws in Starfleet's thinking, and they wanted him to accept something he couldn't. So, he better do more thinking for himself and use the rules and regulations merely as guidelines rather than seeing them as immutable. His "coming out" was the rigging of the test.
When nuKirk rigged the K-M test, he was still making a statement, but for him, I think it was more of a problem-solving stunt, not necessarily a changing point in his life. I don't think nuKirk was ever "positively grim" at the academy and never had the same respect for rules and regulations TOS Kirk had while at the academy. TOS Kirk probably had to think deeply about whether or not to rig the K-M test, while I doubt nuKirk did, because he was probably already more comfortable with such actions and not afraid to be brash.