to play (games, sports); to enjoy oneself; to mess about (with alcohol, gambling, philandery, etc.); to be idle; to do nothing; to meet up (with friends); to hang out
Examples (2 in total)
あなたは彼の気持ちをもてあそんではいけない。
You should not trifle with his feelings.
彼は彼女の事は本気ではない。彼女をもてあそんでいるだけだ。
He's not serious about her at all - he's just playing with her.