Breaking up is hard to do, but it doesn't mean it has to be free from humor.
Does your ex have a bar or a cafe they like to frequent?
Print out a nice, clear photo of the person, add in a nice tagline like, "This woman gave me VD" or perhaps, "This person drove me into bankruptcy" or the ever popular, "This person sucks in bed." Post them in the bathroom. Post them repeatedly until its fairly obvious that everyone the ex might bump into at the bar will have seen the poster.