J.T. makes me think of what’s his name, [name]Jonathan[/name] [name]Taylor[/name] [name]Thomas[/name], that kid from Home Improvement. [name]Way[/name] back in the 90’s…
This is definitely male to me; I actually know people called J.T. or J.D. But then again, I’m from the south, where initial names are a little more common, and, in my grandparents’ generation and before, very common.
A.J. Boy, definitely. You know, almost all of these make me think of a famous person. In the 90’s, mostly. A.J. from Backstreet Boys?
D.J. This one could go either way on gender. Famous person who pops to mind in the older sister from Full House. So, I would lean towards female but wouldn’t be put off by a boy called D.J., either.
P.J. More boy, but could work for a girl as well. Famous reference: The littlest child in the comic Family Circus. I see this as a cute childhood nickname, since I know a lot of people who call theirs pajamas p.j.'s, so I would think it weird to see anyone older then about ten called P.J.
T.J. This is the only one that a famous person doesn’t come immediately to mind. However, it’s also the one I’ve heard most in real life. Definitely male. I went to school with a T.J (I think it stood for [name]Timothy[/name] [name]James[/name], but he was never called anything but T.J.). I also know people who like the sound of T.J. enough that they choose names in order to use this nickname.
G.K. Famous person: G.K. ([name]Gilbert[/name] [name]Keith[/name]) Chesterton, a British writer who wrote the Father [name]Brown[/name] mysteries. So my example is male, but really it doesn’t have much gender to me either way. I can just as well see a girl G.K. ([name]Gemma[/name] [name]Kate[/name]??)
M.J. As has been pointed out before, [name]Mary[/name] [name]Jane[/name] from Spiderman. This is the only one that seems definitively female to me. My cousin had a roommate called M.J.; I’m not sure what it stood for. It’s probably the “[name]Em[/name]” sound of the M that ties it to [name]Emily[/name] that makes it sound more feminine.
Interesting to think about. I certainly know many more men and than women who use initial nicknames.