Trying to decide what the most riotous moment was from Comedy Central’s Roast of Justin Bieber is like choosing your favorite cupcake at Sprinkles in Beverly Hills. You can’t settle on one.  While the roast is a prime platform for stand-ups to bare their best fangs, rarely — if ever — do you see comedic alter egos take the podium. But that’s what happened during tonight’s broadcast when Will Ferrell’s Anchorman Ron Burgundy took a break from “hosting SpikeTV’s Your Mother’s a Fat B**** Award Show” on stage 24 to dress down the pop idol. Burgundy doesn’t seem to mind the work on the SpikeTV kudo show: “Some real, clever writing; great energy over there.”  Let’s roll the videotape on his great moments tonight: