Meaning: Not be serious, play with something
Example: I was MESSING AROUND on the internet because I couldn't be bothered to do any work.
Meaning: Treat someone badly
Example: She is always MESSING me AROUND and never does what she promises.
Meaning: Have a sexual relationship outside marriage or a permanent relationship
Example: She's not faithful- she's been MESSING ABOUT since they got married.
We have 7 phrasal verbs with 'MESS'