Animosity is hatred. If your (supposed) best buddy embarrasses you in front of a big crowd, your friendship could turn into animosity.
Animosity comes from the Latin word animus, meaning "spirit" or "mind." That's also the root of the word animated — literally, "full of spirit." So how did animosity get so negative? Over the centuries, the original meaning of "high spirits" soured into "hatred." Today we most often speak of animosity toward, between, among, or against people. Keeping your animosity in check might make steam come out your ears.