Definition of "act up" [act up]

• To misbehave; to cause trouble. (verb)

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• "When Zoe came to reflect calmly on the occurrences of the theatre night, she was piqued at the tameness with which she had allowed herself to be domineered over by a man whom she had as yet hardly accepted for a lover; she determined that the next time he came, she would assert her own dignity, and act up to her old maxim, that "no man can stand being treated too well"."
• "You knew better than to act up in Miss Hargraves, you knew not to act up in the cafeteria if Miss Hargraves saw you, she'd put that ruler across your head, no matter whose class you was in."
• "Miss Macnulty did not believe in Lady Eustace, and was not sufficiently gifted to act up to a belief which she did not entertain."