I think firing the guy and leaving it at that is the optimal thing for BK to do. Let's agree that it probably won't be cost effective to garnish the guy's wages, in terms of legal costs to take him to court, the potential future income he'll have, etc. On BK's side, there's a lot of risk of negative publicity involved with taking him to court. I don't think being fired is being let off easy - surely this stunt will make it at least more difficult to be hired at another fast-food place.