Mess Around Meaning

(idiomatic) To have a sexual relationship, especially one which is non-commital.

Example:   The kids sat there messing around with leaves and blades of grass because they were bored.
  These guys don't mess around! They finished the whole job in ten minutes.
  Hey, don't take it personally. I was only messing around.
  Don't mess around with electricity if you don't understand it.
  Rumor has it that he's messing around with his secretary.