I think that the word catty is used primarily to describe women's behavior, and (jumping along here) that the behavior in question is a kind of snippy derision of another person, the snippy derision not being seen by the user of the word 'catty' as a sign of power but potentially a sign of weakness combined with a kind of sneakiness, when a man (using this view) would be straightforward at whatever time he might choose to put someone else down, or someone else's ideas down. In this use, catty is sort of like whiney, just the other side of the coin.
Use of sarcasm is similar .. an observation expressed with a certain derisive component. I am not sure why catty is somehow a 'worse' way to be, but it is certainly meant as a negative adjective.
I have heard it said that men are less observing of nuances of social interaction (not so much a view I hold, at least of the men I've known well). The word 'catty' may be a function of men's and some women's distaste for commentary related to others involved in social interaction. Or not. Maybe it's just about the sneakiness-behind the back element.
Joanne--
I've frequently been called a nag, but in my house details don't languish and loose ends are tied up.
I can't say I like the term, but I accept it as descriptive.
