What Does Acting Up Mean?

Act Up Meaning

Definition: To misbehave (of people); to malfunction (of things).

Origin of Act Up

This expression, with the definition of being unruly, has existed since the early 1900s. It is related to the verb act that has existed since the mid 1300s. Act means to do something.

Examples of Act Up

definition of acting outIn this example, a young woman uses the expression while talking about a student in her class.

Cassie: How is your teaching assistant job going?

Rebecca: It’s not too bad. Most of the students are great, and I really enjoy it—for the most part. But there’s one student who is always acting up.

Cassie: Really? How so?

Rebecca: He always is interrupting me, and he is rude to the other students. In the last class, he actually made a paper airplane and threw it at someone in the middle of class.

Cassie: Wow. I didn’t realize people actually did that.

acted outIn the dialogue below, two friends are discussing the engine trouble their car is having.

Antonio: Hey! Do you smell something weird?

Igor: Uh oh. I think it’s my car. I’d better pull over to the side of the road.

Antonio: Hurry up. I think I see smoke coming out from under the hood.

Igor: Yeah. Let me take a look at the engine. It’s been acting up a lot lately.

Antonio: How so?

Igor: Like making weird noises and then not starting. I’m not sure exactly what the problem is. I think I’ll have to take it to a mechanic.

Antonio: You’d better do it soon. It looks in bad shape.

More Examples

The article excerpt below is about a mother who is frustrated because people keep making rude comments about her children.

  • I have three lovely sons – ages 3, 6 and 8. They are wonderful and while they can act up and get in trouble just like any other child (and by child, I mean daughters), they are blessings and I can’t imagine my life without them. –OC Register

This article excerpt is about a school that is trying an innovative way to improve students’ behavior.

  • The principal, teachers, on other staff reward good behavior more than they try to punish students who act up. –OC Register


The phrase to act up describes people, usually children, who are acting stubborn or breaking the rules. It can also describe a thing that isn’t working correctly.