mad dog shitting razor blades
When someone is so bad at staying on topic they might as well be a dog that shat razor blades in your shoe.
You: 'Did you steal my pencil?' Them: 'I was trying to save my dog from a bear.'
You: 'Why did you skip class?' Them: 'I was arguing with my teacher about my dog.'
You: 'Why did you cheat?' Them: 'I was trying to win a bet with my brother.'