I'll get back to you on that one
A lie they tell themselves so they don't have to face the fact that you're the worst and they're the worst for even talking to you.
'I'll get back to you on that one' after you told them you had a robot for a pet.
'I'll get back to you on that one' when you asked if they were still alive.
'I'll get back to you on that one' after you said you could beat them in a spelling bee.'