Saturday Night Live cast member Bill Hader is notorious for losing it during his Stefon segments, but he has a crutch: He can cover his mouth. It all seems like part of the process. At the very least, his crack-ups provoke crack-ups from the audience (and Seth Meyers), and unlike past cast members who broke character (Jimmy Fallon, Horatio Sanz), it somehow works for Hader.
You may recall a recurring skit from the last season of SNL: “The Californians.” During the live broadcast, it was hard enough for Hader and some of the other cast members to keep it together. But in the dress rehearsal, they just let it go. Hader is HILARIOUSLY useless in the skit. Later, even Kristen Wiig loses it. The best bits, however, start around the 0:40 mark, and pick up again near the end, where Hader looks like he’s trying so hard to stifle a laugh he may cry.