Felix has always been attracted to his best friend's girlfriend Rita. From all outward appearances though, Felix seems to really dislike Rita. Felix is likely employing what defense mechanism?

The answer is reaction formation.

Explanation:

Reaction formation is a defense mechanism is which a person exhibits a behaviour that is radically opposite from what he really feels. In the example, Felix shows excessive dislike to hide his true feelings about Rita.

This mechanism is believed to occur because either people are afraid of being discovered, thus negatively affecting their lives; or because they perceive their own feelings as unacceptable and are trying to convince themselves to change.