1. (of a person) behave poorly or inappropriately, (of a thing) fail to function properly
my phone/computer is acting up at the moment
This phrasal verb relates to behaviour or function, whether it is about people or technology. If someone is 'acting up', they are probably misbehaving or disobeying instructions; and if a machine or anything mechanical or electrical, for example, doesn't work properly, you might say that it's 'acting up': "I don't know what's wrong with my computer. It's really acting up this morning. I think I'll just restart it." You can use this phrasal verb in any context, social or professional.