I missed the part where that's my problem
You say this when someone yaps about something you don't give a single shit about and it's not your problem.
'I missed the part where that's my problem' when my teacher kept bugging me about my homework.
'I missed the part where that's my problem' after my cousin said I ruined her party.
'I missed the part where that's my problem' when my friend blamed me for her bad grade.