Not sure if anyone else put this up yet, but here's
Jonny and Benedict presenting at the Oliviers. The darling arm punch is at roughly @3:06. It makes more sense if you start from there (if you for some reason don't want to watch the full clip) because you get to hear the comment from Benedict's "After the Dance" co-star Adrian Scarborough that makes him a bit bashful, thus leading to Jonny's punch on the arm.