If you are an egomaniac, you carry egoism to such an extreme that your needs, desires, and interests have become a morbid obsession, a mania.

The egoist and egotist are obnoxious, the egocentric is intolerable, and the egomaniac is dangerous and slightly mad.

He is the most egocentric person I have ever met.

How egocentric her new roommate is.

Altruism, the philosophy practiced by altruists, comes from one the variant spelling of Latin alter, other.

Altruistic actions look toward the benefit of others.

If you alternate, you skip one and take the other, so to speak, as when you play golf on alternate Saturdays.