I don't rightly know
A stupid excuse for not knowing something. Like when you're too dumb to answer a question, but you don't want to admit it.
'What's 2 + 2?' 'I don't rightly know. I was too busy counting my toes.'
'What's your favorite color?' 'I don't rightly know. I was too busy being a moron.'
'What's the weather like?' 'I don't rightly know. I was too busy being a fool.'