Green’s Dictionary of Slang

act up v.

1. to make a fuss in order to attract attention to oneself.

[US]J.W. Carr ‘Words from Northwest Arkansas’ DN III:i 68: act up, v. To show anger in an unbecoming manner. ‘You needn’t act up, even if you don’t like it!’.
[US]D.G. Phillips Susan Lenox II 213: Don’t mind him [...] He’s only acting up queer.
[US]F. Klaeber ‘A Word-List From Minnesota’ DN IV i 10: act up, v. To show off, or just to act in a care-free, happy-go-lucky way, or to act in a foolish, silly manner. ‘The children always act up with him.’.
[US]J. Lait Broadway Melody 86: Eddie had acted up mightily.
[US]L. Hughes Mulatto in Three Negro Plays (1969) Act I: De way he’s acting up can’t go on.
[US]Botkin Lay My Burden Down 117: They act up and say they don’t have to take off their hats in the white stores and such.
[SA]H.C. Bosman Cold Stone Jug (1981) II 137: Act up as if you’re screwy. But not too much, mind. Just enough to get the old horse-doctor really interested in you.
[US]‘Hal Ellson’ Tomboy (1952) 110: We got word that the Eagles are acting up.
[US]D. Goines Street Players 181: All of a sudden they start acting up in the front seat.
[US]N. Pileggi Wiseguy (2001) 66: They would discuss [...] how the kids acted up.
[UK]N. Cohn Yes We have No 129: One night, legless, she started acting up.
[UK]M. Collins Keepers of Truth 272: They were acting up for the camera.

2. to cause (someone) trouble.

[US]A. Adams Log Of A Cowboy 275: The horse of some peeler, working with one of Shanghai Pierce’s herds, acted up one morning and fell backward with him.
[US]H. Green Maison De Shine 270: Has Bill been actin’ up ag’in?
[US]P.A. Rollins Cowboy 76: The outlaw he began to throw talk. The ranger he said: ‘Don’t act up. Be sensible and come along with me.’.
[US](con. 1944) N. Mailer Naked and Dead 543: Ah wish to hell that hole in mah belly would stop actin’ up.
[US]B. Spicer Blues for the Prince (1989) 27: Is your back acting up again?
[UK]P. Barnes Ruling Class I vii: The ol’ lumbago’s acting up again.
[US]N. Thornburg Cutter and Bone (2001) 9: So the old stomach acts up again — so you get wound up — so what?
[US]A.K. Shulman On the Stroll 8: His stomach, which had kept him from signing up for another hitch at sea, was acting up all the time now.
[Ire]R. Doyle Snapper 178: I was just readin’ there yesterday abou’ how sometimes your hormones start actin’ up when you’re pregnant.
[US]J. Lerner You Got Nothing Coming 53: Cain’t a muthafucka make hisself a phone call without y’all acting up and shit?