act_up
1. [ verb ] misbehave badly; act in a silly or improper way
Synonyms: carry_on
Examples:

"The children acted up when they were not bored"

Related terms: misbehave
2. [ verb ] make itself felt; as of recurring pains
Synonyms: play_up
Examples:

"My arthritis is acting up again"

Related terms: ache
Similar spelling:   act_upon