I don't #
It means you're as dumb as a bag of rocks. Your friends don't know anything either. You're all just a bunch of morons sitting in a room going, 'I don't #.'
"I asked my friends what I should add. They said, 'I don't #.'""
"He asked his friends what they thought. They all said, 'I don't #.'""
"We all sat there in silence. We all said, 'I don't #.'"