I missed the part where that's my problem
You throw this at someone when they bring up something you don't care about and it's not your damn problem.
'I missed the part where that's my problem' when my mom asked why I didn't call her for three days.
'I missed the part where that's my problem' after my brother blamed me for his failed relationship.
'I missed the part where that's my problem' when my friend asked why I didn't help her move.