Will Ferrell and Paul Rudd heckling a singing Jimmy Fallon makes for one seriously hectic skit

Sheer chaos. When you have Will Ferrell and Paul Rudd together in a skit, it doesn't really matter too much what the thing is actually about. It's going to be funny regardless. That was certainly the case on Thursday's Tonight Show, when Anchorman pals Rudd and Ferrell played audience members heckling …