I only use those phrases very rarely , but to me they mean: (and I think that they apply equally to men and women).
High maintenance: A set of behaviors: Need things, in particular gifts / favors. Flowers are a *requirement*, not something that is met with happy appreciation. Need sex, back-rubs, something. Constantly needs help with something, but doesn't provide help in return. A general helplessness. Flat tire - call partner to leave work and drive over to help, rather than call a tow truck. Computer broken - call partner to fix it, even though they write software for a living. Family problems, need partner to help - which is fine, but not if they don't reciprocate.
Nagging: Constantly telling someone to do something when they already know, and either have it lower on their priority list, or have decided not to do it. Often coupled with thinking that their own set of priorities for chores should take precedence over their partner's priorities. Usually coupled with treating the partner like a child: "What, you haven't taken the trash out yet - *sigh*, I'll do it". (when it fact their partner is busy with something that may be equally or more important.
I think there is a lot of variation on how these terms are used, but I see both are a form of viewing their partners as servants, not equals.
As I said, I use these rarely, and think that they apply to men and women who exhibit these sorts of behavior.
Can anyone define "high maintenance" and "nagging", those words are thrown around very casually by men and I have always wondered how they define them.