To put it simply, "acting out" is a phrase people will use to describe when they're indulging in some sort of negative behavior (or something that they think is a negative behavior) because of a particular uncomfortable feeling.
Although the phrase is tossed around in meetings with such abandon one would think that it was coined in a 12 Step environment somewhere, it's actually a term from the therapeutic world, and has varying interpretations when considered in the different contexts of parenting (children's tantrums), psychotherapy (the struggle to act on desires forbidden by the Super Ego and yet desired by the Id), criminology (anti-social behavior as a motive for criminal acts) and yes, addiction. (Tantrums, forbidden desires, anti-social behavior -- gosh, we're always found in such good company, aren't we).
In addiction "acting out" is a compensating behavior. One way to look at it is that we relieve stress by substituting a behavior for a feeling:
"I had that big job interview late in the afternoon so after lunch I went to the candy aisle at the supermarket and really acted out."
"I saw my ex with their new date last night and I couldn't get it out of my head. This afternoon I took the credit card I had just finished paying down to Saks and completely acted out."
"I was so stressed about my appearance in court that when that guy cut me off on the freeway this morning I totally acted out. I must have chased him for three exits trying to catch him and flip him off."
In my humble opinion, kids, I think we begin to do ourselves a disservice by over using what is essentially half a phrase.
"Acting out" has become vague shorthand for any number of behaviors and feelings. If the point of self examination, be it sharing at group level, with a sponsor, or via some writing (an inventory, journal, etc.) is clarity, then by not finishing the phrase "acting out" I'm keeping myself unclear about what was driving me.
For myself, I try to name what I was acting out, and be specific:
I acted out my panic that I would make a fool of myself in the interview by practically inducing a sugar coma when I inhaled a giant bag of M&M's. Wait. I lied. Two bags.
When I saw my ex it brought up all the old jealousy and rejection, so I acted all that out by shopping myself back into major debt in one short afternoon.
I had so much fear and anger about my court date that I totally acted it out by chasing the driver who cut me off across multiple lanes for three exits, just to try and flip him off.
My point is not that you should have some sort of formula for what you say; nor am I trying to tell you what or how to share. My point is that if I'm going to be as honest with myself as I possibly can be (and honest with others in an effort to be of service to them), then I need to get in the habit of connecting the dots when I speak about what I'm feeling and what I'm doing.
Sometimes I believe it's possible for me to act out and not even know what I'm acting out over -- it can be difficult for me to see, for myself, the cause/effect of the (scary/negative) feeling and the compensating/acting out behavior. And this problem is intensified when I am lost in the guilt or self-loathing that repeatedly acting out in the same self destructive way might bring. I'm so busy feeling terrible about over-(younameit)-ing that it can be even harder to see what triggered me. The "feeling terrible" part (guilt, and it's snarky cousin shame, and my arch-nemesis, fear) thwarts calm, rational reflection and eventual insight.
(Or, in an even more insidious twist, the self loathing and remorse that comes from the self abuse of continuing to "act out" in a certain way actually becomes a form of self obsession -- and alcoholism is a disease of self obsession, so the more that I'm fueling my self obsession the more I'm fueling my alcoholism. Gah! What a nightmare! Hold me, I'm scared!)
That's where sober friends, a sponsor, and a regular written 10th Step (Step 10: Continued to take personal inventory and when we were wrong promptly admitted it) can make all the difference in the world.
We all need help looking at our stuff sometimes -- it's a "we" Program, after all -- and I believe it when they say that partly why AA works is that we're not all sick on the same day.