- The way Marcus's dad shows absolutely no interest in him in "About A Boy's Dad".
- Marcus complaining to Will that he drove away the three False Friends, despite knowing those three were just using him for their own ends. The boy was so lonely that he saw getting bullied as a better alternative to being alone!
- Just everything about Marcus and Fiona's situation, especially with the poor kid sitting there watching his mother crying at breakfast and being totally unable to help her. Later he panics about how even his mother is feeling better "at the moment", he has no way of knowing when she'll plummet into another depressive episode again. Then she attempts suicide, leaving him with the genuine fear of being abandoned during his time of need.
Tear Jerker / About a Boy