fool around

1. Engage in flirting or casual sexual acts; also, engage in adultery. For example, He caught the two teenagers fooling around in the basement . [1830s]

2. Also, monkey around . Engage in idle or casual activity, putter. For example, Jim loved to fool around with his computer , or She was monkeying around with some figures in hopes of balancing the budget . [Second half of 1800s]

3. Engage in frivolous activity, waste time. For example, Instead of studying, he spends all his spare time fooling around . Also see fool away .