I found this on Personality Nation by NightSkyGirl a while back. Related to ennegram.. but i think these concepts themselves should be considered individually, because I would bet that most people have fallen back on more than one of them.
Ones - Reaction Formation
"where unacceptable urges or emotions are replaced with opposite acceptable behaviors." -- NightSkyGirl
Reaction Formation is a defense mechanism by which individuals reduce or try to eliminate anxiety caused by their own thoughts, feelings, or behaviors that they consider unacceptable by responding in a manner that is the exact opposite of their real responses. The One’s active inner critic dictates what is acceptable based on social mores, contextual expectations, and moral principles, and reaction formation becomes a defensive remedy when Ones experience what they deem “unacceptable†reactions. A subtle example often seen in Ones is when they dislike someone yet are especially nice and polite to this person. A more blatant example – one that is not exclusive to Enneagram style Ones – is an individual who crusades against corporate corruption, only to be discovered later as having embezzled money from the organization.
Twos - Repression
"where personal desires and needs are excluded from conscious awareness." -- NightSkyGirl
Repression is a defense mechanism by which individuals hide information about themselves from themselves – for example, feelings, desires, wishes, aversions, fears, and needs – that are too difficult to acknowledge consciously. However, the repressed information doesn’t disappear; instead, expression of the repressed data is controlled or held down while it continues to influence the individual’s behavior. For example, Twos may feel anxious and need reassurance, but they may be only minimally aware of this. Instead of exploring these feelings or seeking comfort, the Two reassures another person who appears to be in distress.
Threes - Identification
"where the self-image models the expectations of others." -- NightSkyGirl
Identification is a psychological defense mechanism in which a person unconsciously incorporates attributes and characteristics of another person into his or her own personality and sense of self. Identification is a way of bolstering one’s self-esteem by forming an imaginary or real alliance with an admired person, then taking on that person’s characteristics. When Threes model their own behavior after someone else or the idea they have of someone, they are usually not aware they are doing so. For this reason, it becomes complicated for them to untangle who they really are from this image. In particular, Threes identify most with images of individuals who are admired in the Three’s desired social context, and the image with which Threes identify often changes as their context changes.
Fours - Introjection
"where aspects of the external world and other people are integrated into the self." -- NightSkyGirl
Introjection is a counter-intuitive defense mechanism. Instead of repelling critical information and negative experiences that can cause a person anxiety or pain, individuals introject the information – that is, they fully absorb, internalize, and incorporate these data into their sense of self. Fritz Perls, the father of Gestalt Therapy, refers to this phenomenon as swallowing something whole without being able to differentiate between information that is true from information that is untrue. Fours introject negative information – and repel positive data – about themselves as a way of coping with painful information and neutralizing external threats. They prefer to deal with self-inflicted damage rather than having to respond to criticism or rejection from others.
Fives - Isolation
"where emotion is detached from a situation in favor of intellectual content." -- NightSkyGirl
Isolation occurs in Fives as a way for them to avoid feeling overwhelmed and empty. Fives isolate themselves by retreating into their minds, cutting themselves off from their feelings, and compartmentalizing – that is, isolating each part of themselves from the whole or the related parts. For example, Fives separate their thoughts from their feelings and/or feelings from behaviors, as well as separating their personal and work lives. Fives may also isolate themselves from other people and separate their relationships so that their friends never meet one another; in fact, some Fives even have secret lives.
Sixes - Projection
"where unacknowledged self motives, feelings, and thoughts are attributed to others." -- NightSkyGirl
Projection is a psychological defense mechanism in which individuals unconsciously attribute their own unacceptable, unwanted, or disowned thoughts, emotions, motivations, attributes, and/or behaviors to others. While the projection may be positive, negative, or neutral, it occurs because the individuals who are projecting perceive the projected attributes as difficult to acknowledge or threatening to believe about themselves. Because Sixes make these attributions unconsciously, they imagine that they are true, although at a deeper level they are not entirely certain about this. Although Sixes use projection as a way to create some certainty and thus reduce their anxiety in ambiguous, uncertain, or potentially dangerous situations, these projections – particularly if they are negative in nature – ironically raise the Six’s anxiety level. In addition, when Sixes project either something negative or positive that is untrue, they create a false reality without knowing they are doing so.
Sevens - Rationalization
"where unacceptable motivations for an attitude or action are reframed through good reasoning." -- NightSkyGirl
Rationalization is a defense mechanism by which individuals explain unacceptable thoughts, feelings, and behaviors in a way that entirely avoids or obscures their true motivations, intentions, or the effects of the behavior. When Sevens rationalize, they do so by positive reframing, justifying their behavior by explaining it in highly positive terms. Sevens use reframing to avoid pain, discomfort, sadness, guilt, and anxiety, as well as to avoid taking personal responsibility for what has occurred.
Eights - Denial
"where emotions or sensations of weakness are not acknowledged." -- NightSkyGirl
Denial is a defense mechanism by which individuals unconsciously negate something that makes them feel anxious by disavowing its very existence. These can include thoughts, feelings, wishes, sensations, needs, and other external factors that are unacceptable to the Eight for some reason. Denial comes in a variety of forms. A person may deny the reality of the unpleasant information altogether, admit that something is true but deny or minimize its seriousness, or admit that both the information and its severity are true but deny any personal responsibility for it.
Nines - Narcotization
"where conflict and discomfort are avoided through self-comforting activities and routines." -- NightSkyGirl
Narcotization is a psychological defense mechanism in which individuals unconsciously numb themselves to avoid something that feels too large, complex, difficult, or uncomfortable to handle. Nines narcotize and distract themselves by engaging in prolonged rhythmic activities that are familiar, require very little attention, and provide comfort – for example, washing the dishes; working in the garden; continuous pleasure reading of books by the same author or within the same genre; going for a walk or a bike ride; engaging in frequent or extended casual conversations; or continuously changing channels on the TV. Nines also use daily routines such as morning or evening rituals to immunize themselves from being fully aware, and they feel agitated, irritated, or disoriented when these repetitive activities become disrupted.