That is the question when it comes to a typical FLR (Female Led Relationship). But there is another question involved here, and that is: What do you mean by “Be Mean?”
There are two completely different meanings to the the term “Be Mean.” The first, and most obvious, is to act like a “Bitch” toward your partner. You know, paddle him a lot just because you can, and order him around as if he doesn't really matter in the great scheme of things. And there is the other meaning... To do things to him that he will enjoy (for one reason or another), but that only “seem” to be mean.
Let me explain. When a man asks his wife/mistress to be “mean,” what he probably wants her to do is to find ways of teasing or tormenting him that will push his limits. For example, make him spend a longer period of time in chastity, or maybe spend more time doing chores (naked?). He may want her to punish him more harshly, but she still doesn't have to be a “Bitch” about it.
Of course, there are those men who enjoy being abused by a woman who gives him no room to breath, no affection, and no leeway when it comes to obedience. But most men don't want (or need) to be treated that way.
Another, more subtle meaning, can be that he wants you to humiliate him in some way. Belittling him, or making him do embarrassing things, maybe even in front of other people. Many men have fantasies that involve being humiliated in one way or another. So "Being mean" may simply mean that he wants you to cause him more embarrassment from time to time.
Let's face it. Most FLR's are based on love, not brutality. So the next time your partner asks you to mean, ask him to be more explicit about what he wants you to do. Ask him for some examples. Does he want you to treat him like dirt, or is he looking to have his limits pushed a bit more? Clarity can make all the difference.