Meaning: Not be serious, not use something properly
Example: The children were MESSING ABOUT with the TV remote control and broke it.
Meaning: Treat someone badly
Example: He is always MESSING me ABOUT and never does what he promises.
Meaning: Have a sexual relationship outside marriage or a permanent relationship
Example: He's not faithful- he's been MESSING ABOUT since they were married.
We have 7 phrasal verbs with 'MESS'