@dgreater
there is a reason why points #3-5 exists. Without those, you would be including a whole bunch of characters that people don't call tsundere. I have listed before just a small summary, but here's an indepth explanation.
Reason for #3 (tsun and dere must be drawn out by the same thing)
Nanoha, judging from the first season alone, is tsuntsun to the villain yet deredere to her friends. Nanoha = tsundere then?
If the tsun and dere aren't drawn out by the same entity, one would encapsulate the vast majority of anime protagonists as tsunderes. This is because in a typical show, the protagonist is usually very tsun to enemies and very dere to friends.
If anything, this is the 'rule' that people should include in their definitions of tsundere, because without it, they'll include a vast amount of characters that the majority of people don't consider tsundere.
Reason for #4 (tsun is the cause of the need to hide dere)
First of all, if tsun isn't caused by dere whatsoever, then people don't term that as tsundere at all.
Or these characters are termed yangire, where their tsun is caused by some other event that 'snaps' them out of their normal selves into their tsun mode.
For example, Ryuuguu Rena of Higurashi, who's famous for 'snapping' from her dere omochi-kaeri-mode into her dreaded oyashiro-mode and back. And I don't see anyone labelling her as a tsundere.
So we established that tsun must be the cause of the dere. But there's another group of characters who also acts tsun as the cause of their dere, and that's the yandere girls. But what's the difference between a yandere and a tsundere? Simple, yandere almost always use their tsun to SHOW their dere, while tsundere use it to try and HIDE it.
For example, without this, Fuyou Kaede from Shuffle and Kotonoha/Sekai from the infamous School Days would be considered as tsundere as well. All these characters exhibit tsuntsun and deredere behaviour, but people don't consider them tsundere.
Do note that the rule doesn't say 'all tsun must be used to hide dere'. A lot of tsunderes use their tsun side for other good reasons on the same character they're dere for, but I have yet to find a character people call a tsundere that doesn't try to hide their dere with their tsun in some way, shape or form.
[as an aside, people I know try and differentiate tsundere and yandere in saying tsundere is tsun on the outside and dere on the inside, while yandere is the otherway around.
Of which I counter, then what about the tsunderes who's usually dere then turn tsun, like say, Kaname Chidori of FMP fame? She's usually neutral or dere towards Sagara, and only turns tsun if either he gets too close to Tessa or he's doing something mighty stupid again. She's certainly not yandere...]
Reason for #5 (tsundere activities must be occasional)
This is mainly my 'get out of jail' card, because there's a character out there somewhere who'll possess all 4 qualities yet they only do that in one occasion. Hardly a tsundere at that.
Let me ask you, do you consider Kana, Nanoha, Rena, Kotonoha, and Sekai as tsunderes? Going by your defintion, they are tsunderes because their tsuns are very evident, and so are their deres. And God knows that there's some sort of catalyst that brings out both tsun and dere.
If you do consider them as tsunderes, then I have no problems. But if for some reason you don't consider even one character as a tsundere, then your defintion of tsundere needs to be revamped.
That's really the problem I see with the definition of tsundere running nowadays; with ill-defined definitions, those definitions are so broad that they could describe characters people don't consider tsundere at all. But if they're fine with that, then there's nothing I can do about it.