to act on the spur of the moment

to act impulsively

I’ll act on your advice

to act as if one owns the place

to act cool

to act in bad faith

to act in good faith

to act out of character

to act stupid

to act the big shot

to act like a madman

to act the fool

to act the goat

act of God

to act up

act of grace

Act rather than give up hope!

to act as interpreter

to act as if nothing had happened

to act in concert

to act as opponent

to act on instinct

Act your age!

to act like a prima donna

to act as a pagan