a (idiomatic|drama) Not in character; not successfully performing within the mindset of a given character in a theatrical performance. See also (term|break character), (term|drop character).
a (idiomatic|drama|role-playing games) Not acting; not "on"; behaving within one's natural personality rather than that of a character, or taking actions entirely outside the fictional context.
a (idiomatic) In a manner inconsistent with one's usual and expected personality or behavior.