Act foolishly—act without reason or good judgment.
- She acted foolishly in her business dealings, trusting the wrong people or not trusting her employees enough.
Act the fool—(also: play the fool) deliberately act so as to appear eccentric or foolish.
- He was a small, puny lad who acted the fool to stop himself being bullied.
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.