Pascal's Triangle Revisited - S1-E25
Corrected entry: When the Dean is telling Jeff and Annie about the dance, you can see that the buttons on his shirt are already undone so he can more easily pull it open to show Jeff his 'all 5 dances' t-shirt underneath.
Correction: That was his intention all along. He adores Jeff and always wants to either touch or impress him, so it's nothing out of the ordinary for his character.
Knever