It sounds like you get caught between two people who can be lazy and disrespectful. And both tend to make you the fall guy. If it’s ongoing then you need to sit down with your boss and tell him you no longer want to bear the burden for another persons lack of respect and how can “we” change this problem and “manage” it differently? If it’s his job to Manage then HE needs to remove the pattern where an employee is asked to do something through you or someone else and fails to do as asked.

The other thing you can do is write a memo and date it and copy both your manager and the person who is asked to present something for work through you. Having it in writing and dated and copying it to both parties keeps the task up to these two individuals and keeps you from being scapegoated. 😉