Following are some of the most commonly used defense mechanisms:
Denial - Refusal to accept reality because it is too threatening.
Distortion - Reshaping external reality to meet internal needs.
Delusional Projection - Frank delusions and paranoia about external reality (can be persecutory).
Fantasy - Retreat from reality into a fantasy world in the hope of resolving internal and external conflicts.
Projection - Attributing unacknowledged feelings on others (prejudice, jealousy etc.).
Hypochondriasis - Transforming negative feelings towards others into negative feelings towards self (pain, illness, anxiety).
Passive Aggressive Behaviours - Indirectly expressing aggression towards others (for example through gossip).
Acting Out Behaviours - Expressing unconscious impulsive emotions or wishes.
Intellectualizing - Disconnecting emotion and ideas.
Repression - A lack of awareness of underlying ideas and emotions.
Reaction Formation - Opposite behavior to what you want or feel.
Displacement - Putting intense emotion on the wrong thing or person.
Dissociation - Drastically but temporarily change personal identity or character to avoid distress.
If you or someone you care about is using any of the above defense mechanisms in an unhealthy manner you may wish to consult with a clinical psychologist. S/he will help you understand what is going on and how you can make good choices that will improve both your relationships and your health.