I'm actually amused at finding this thread again (unintentionally, actually), because I have just commited a big one myself in my own writing for Steve's upcoming new show.
This one is done a lot more in children's fair (even though I'm not doing kiddy shows): one of the kids of the show develops a crush on a grown-up of the opposite sex in their life (a teacher, a mentor, someone from the neighborhood, etc), but the kid becomes devastated when he/she sees that the grown-up he/she has a crush on has a boy/girlfriend, or is getting married, etc, then the grown-up gives the kid a lecture on "different kinds of love" and tells that kid that one day he/she will find someone his/her own age, etc.