A cause of Reaction Formation is when a person seeks to cover up
something unacceptable by adopting an opposite stance. For example
the gay person who [...] may be concealing their homosexual reality.
This may be a conscious concealment but also may well occur at the subconscious level such
that they do not realize the real cause of their behavior. Reaction Formation thus can turn
homosexual tendencies (love men) to homophobic ones (hate men).
Freud called the exaggerated compensation that can appear in Reaction Formation
‘overboarding’ as the person is going overboard in one direction to distract from and cover
up something unwanted in the other direction [...]

http://changingminds.org/explanations/behaviors/coping/reaction_formation.htm