I still say every character in "Peep Show" embodies an aspect of David Mitchell's psyche. My interpretation of this scene is that David Mitchell was trying to lose weight, and is mad at himself for eating a donut.
love the show and have been following it for years - also love this clip. however, i've got to say that season 8 has been a disappointment. they've roped both characters into the whole dobby situation instead of giving Jez and Mark separate romantic focuses. i hate to say it, but it looks like they've run out of ideas... :(