Mostly pulled from my own personal Ten-canon, plus
the site that owns my soul and some extras from my friend's series 3 box set. :D
1) Believe it or not, Ten was/is one of the only Gallifreyans to have nightmares.
2) Back in the Academy, the Doctor and his little circle of friends, including the Master, were generally pranksters. Once they trapped their teacher in a time loop for hours so that he taught the same lesson for an entire day.
3) While it is very well known that Ten likes bananas, he hates pears.
4) Ten still loves and misses Rose dearly. However, he's working on the reasoning that a) he remembers what it was like being Nine, and it was very depressing, b) his past self acted first, the lucky bastard, and c) Rose has got enough on her plate without two versions of the same man fighting over her. That doesn't mean that when he next gets a chance, he's not gonna kiss her. As a self preservation thing.
5) Ten got bad marks in nearly all his subjects at the Academy and actually failed one of them 3 times before passing. And just look how he turned out. XD
6) If you get a load of Ten-babble, it generally means one of two extremes: that he's comfortable with you, or that he is extremely uncomfortable.
7) Despite popular belief, Ten actually has tried to tame his hair before. It ended up looking absolutely awful, so he gave up.
8) Ten's TARDIS is a Type 40, which by the time he "borrowed" it was obsolete. He actually saved the old girl from becoming scrap. Interestingly enough, one of the main complaints about this model was that the kitchen was too far from the control room.
9) Ten is a big fan of Earth punk rock - the old stuff, not what they're churning out these days. ;]
10) The chameleon circuit on his TARDIS is actually partly functional now. He just likes the ol'police box the way it is. It's iconic.
11) He doesn't actually believe that Caan will manage to raise his new kids. Or at least, he really really hopes not. He's still waiting on the teenage rebellion he knows will come.
12) The void glasses? Started life as an ordinary set of 3-D specs. Ten jazzed them up a bit.
13) Ten is a total Disney fanboy at heart and keeps the entire animated collection hidden in a safe place inside the TARDIS.
14) The reason Ten got so uptight when Mirage started taunting him about the Master was because deep down, he's terrified that they're as alike as she insinuated.
15) Speaking of the Master, Ten honestly hasn't given up on him and probably never will. He honestly still believes he can save him. Also, he's refraining from jumping on the Koschei bandwagon because he reckons someone needs to cling to the moral high ground. (But he has been so, so tempted.)
16) When Ten's saying that he can't cook, he's telling the truth. Soon after regenerating he tried to cook something up, and almost destroyed the kitchen. He's since then made a way of living on anything that doesn't take longer than 10 minutes. This includes takeaways.
17) As you'd expect from a 903 year old who can change his face, he's had plenty of time to adjust to both other's sexuality and his own (and since even that's liable to change slightly when he does, he has to be pretty well adjusted.) If you wanted to attach a label to him in that odd human way [;-)] I'd guess you'd call him bisexual. But really, he just likes what he likes.
18) In regards to the comm, he looks at Jordan as a sort of little brother, almost, and Chloe as both a source of amusement and a possible companion. He also likes Haruhi a lot. Mostly he admires these guys for their sheer open-mindedness and quirks, although Jordan's position as Oban's Avatar also impresses him. (I'm not actually sure if he's close enough to anyone else to comment! XD)
19) He isn't lying when he says he misses his home planet and the feeling of just knowing that there's other Time Lords out there. However, what he doesn't mention is that he doesn't miss the pompous, stagnant society or the way things were run. Whenever he catches himself thinking this he feels sick with himself. So he doesn't catch himself thinking it often.
20) Speaking of nightmares and the Master, his greatest, unspoken fear is going insane. Occasionally, he has nightmares about it.
Apparently I lied and couldn't be bothered to think of 20. XD Oh well~