Overt expression of destructive or otherwise anti-social impulses in order to express one’s emotional conflict (which can be conscious or subconscious).
Example: A teenage boy with problems at home and a history of behavioral issues comes up behind a girl he doesn’t know very well and grabs her bottom.
Grinnell, R. (2008). Acting Out. Psych Central. Retrieved on October 8, 2015, from http://psychcentral.com/encyclopedia/2008/acting-out/