The term 'HORSE AROUND OR 'RAIN CATS AND DOGS'' is an IDIOM meaning to act in a wild or chaotic manner. It is derived from the phrase 'raining cats and dogs, ' which is used to describe a heavy downpour of rain. The phrase 'horse around' is also used to describe someone who is being mischievous or acting in a disorderly way. Both phrases are used to describe a situation that is out of control or chaotic.