1
general::
Fool or play around, engage in horseplay, as in The boys were goofing around in the schoolyard. [Slang; 1920s]
American Heritage Idioms
2
general::
Phrase(s): goof around
to act silly. • The kids were all goofing around, waiting for the bus. • Stop goofing around!
McGrawhill's American Idioms And Phrasal Verbs