unfavorite

Adjective

 * 1)  Not preferred; in particular, especially disliked.

Noun

 * 1)  Something that is not a favourite; particularly something that is especially disliked.

Usage notes
Most often used in explicit contrast to, as in “These are some of my favorite and unfavorite things”.

Verb

 * 1)  To remove from one’s list of favorites.
 * How do I unfavorite a tweet?