A dictionary of Confusable Phrases: More Than 10,000 Idioms and Collocations

Note:
The expression is not equivalent in meaning to the phrase
make a fool of oneself
— act in a way that makes a person appear
ridiculous or stupid: My advice to you is to refrain from making
careless comments, for you’ll only make a fool of yourself.
act of God • action of God
act of God —
1
. (legal) the action of forces uncontrollable by
man, such as hurricane, etc.: In the event of an act of God,
the school reserves the right to suspend training. 2. said of the
work of God in creation: The doctrine regarded our a priori
ideas as infused into the intellect by an act of God.
action of God —(also: work of God) = act of God 2: Crea tion
is the origin of the totality of the universe by the action of
God.
act one’s age • show one’s age
act one’s age —behave in a manner appropriate to one’s age
(often used in asking children to act in a more grown-up fashion):
She doesn’t look or act her age, she has no gray hairs, not even
crows feet.
show one’s age —show signs of being old: Booth is starting
to show his age. His face is deeply creased and lined, and his
voice has gotten mushy and lispy.
act something out • outact someone
act something out—give expression to thoughts, unconscious
fears, etc. in one’s actions and behavior: Children often act
out their troubled feelings in their games.
Note: 
The expression does not correlate in meaning with the
intransitive phrasal verb act out— behave anti-socially or mis-
behave: The child with a learning problem may act out to di-
vert attention from, for example, his inability to read.
outact someone —surpass another person in acting or per-
forming: The man can outact just about anybody out there.
His prime example is his portrayal of Rollins in Devil in a
Blue Dress.