What do you know -- my son was happy when I got home from work last night!  I told him he seems to be following a pattern:  if he's cranky in the morning, he's happy in the evening & vice versa.  At least for now.  Teens are unpredictable, right?
Anyway, he went to youth group (3 weeks in a row now).  I think part of the motivation is that at the end, they have a "cafe" where they can buy good, greasy appetizers (waffle fries, fried mozzarella, etc.).  Heaven for a teenage boy's appetite!