Yes, I know, two angry posts in a row, meh. I need a specific reason to post, and I haven't had enough time or money to get new gmaes recently (although someone did give me a copy of Dead Island so I might review that-- the few hours I have spent on it have been quit enjoyable, albeit a bit ), but still-- I'm getting a bit tired of this.
A woman who is a nice person generally, and who says something harsh, is not a "tsundere". The term and concept for "Tsundere" came about because Anime writer shave no damned clue how to write women, and so they almost always wrote about a plucky girl or about a proper housewife. Tsundere was an attempt to deepen the female characters by adding one (1) new element of their personality-- usually a mean streak on an otherwise nice girl. However, it is still lazy writing, because the "tsundere" character is almost invariably very, very shallow. The term itself comes from "tsuntsun", IE aloof or irritable, and "deredere", IE lovestruck. And its use goes way too damned far for such a lazy, condescending term.
Unfortunately, Japan being what it is (royally fucked up), and Japanophiles being what they are (also royally fucked up), the term has been used to describe real people instead of half-assed constructs by lazy writers. A normally nice woman who is groped and tehn gets mad about it is called "tsundere". Because... what, she's supposed to LIKE having her breast grabbed by impetuous little turd of a man or something? The man DESERVES the anger. She isn't being tsundere, she's defending herself from an asshole. Similarly, if one percieves a woman as a mean bitch but then sees her doing something nice, this also desn't mean she's a tsundere either. More likely than not it just means that you probably gave her no reason to like you in the first place, or the time you've known her she has been in a situation that you keep caching her in a bad mood due to reasons enitrely beyond her control.
People are more complex than anime constructs. There are a wdie variety of different personality quirks in a single person, and attempting to define them by comparing them to definitions of pop culture concepts is a stupid endeavor. Get to know them as people instead, and you'll find that they're far more interesting that way.