I can't imagine anybody who does not use defense mechanisms. I don't really know the psychological lingo for it, but I just call it being "defensive." People are liable to do it when they are criticized by someone. Their initial reaction is to repudiate the criticism without really considering whether or not it is justified. Thye also don't tend to take the other person's point of view into consideration unless they consciously force themselves to do it.

I think my biggest one is devaluation.  I know that I have real flaws in my personality.  But instead of dealing with them, at times I tend to play them up as a way of pretending to deal with them.  If I make them seem like a joke then I don't have to deal with them on a serious level.

it seems as though most living things are programmed with the 'fight or flight' response, and certainly human nature is no different. 

My biggest defense mechanism would definitely be the 'flight' route!When faced with difficulty or unlooked-for conflict, I prefer avoidance of the situation.  I would rather ignore or excuse myself from it!  This has some advantages, such as allowing me to regroup and decide the best course of action with a clear head, but my 'flight' mentality can also be decidedly unhealthy.  For example, when I started to experience back pain with increasing regularity, my first instinct was to ignore it!  I didn't want to have to think about the possibility that there might be something wrong with me, so it was easier for me to pretend everything was okay.  A week later I was in the hospital with an obstructed kidney stone.  Not my best moment. 

I am definitely aware of my 'flight-mode' or nonconfrontational behavior.  It's one of those things that I have to force myself to be objective of the situation, and ask myself--"Is this something I should ignore?"