Successful revenge. Received retribution for being hurt, physically, financially or emotionally.  This phrase suggests someone embarrassed you and produced laughs among them and others, so now you have sought vengeance by an endeavor that has allowed you and others to laugh at that person. (Compare to Payback.)

“The boss fired me for telling the police about his illegal maneuvers, but I got the last laugh when I saw him sentenced to  jail in a court of law.”