The following is taken verbatim from a letter I wrote to the New York Times on July 31st, 2013, in response to an article where the author spoke to the desirability of asexual dressing and avoiding being nice just for the sake of smoothing social interactions:

Credible feminism drives equality of power, pay, opportunity, and recognition. It's not about wearing pants to deny or distance gender. Men and women are naturally and irrevocably different in their sexuality: behavior that celebrates this — including that which drives sexually tuned plumage — is not only reasonable, it is healthy.

Women will never bridge the very real gap by attempting to subvert their own sexuality, because in doing so, they cede many cues of desirability to others.

The same thing applies to "nice." Nice people are selected ahead of others for many roles simply because it is perceived that it will be more pleasant to be around them. If you eschew "nice", you cede yet another social slice of desirability to others.

In either case, such a choice is completely up to the individual — but the consequences won't be.