1. He's such a dunderhead, always making the same mistakes over and over again.
2. I can't believe I have to work with that dunderhead on this project.
3. Don't listen to him, he's a dunderhead who doesn't know what he's talking about.
4. The boss promoted that dunderhead to a higher position, much to everyone's surprise.
5. I can't believe I have to explain this to you again, you're such a dunderhead.
6. He may come across as a dunderhead, but he's actually quite knowledgeable in his field.
7. I can't believe I let that dunderhead convince me to invest in his business.
8. If you keep acting like a dunderhead, no one will take you seriously.
9. The dunderhead forgot to save his work before the computer crashed.
10. She had to deal with a dunderhead customer who couldn't understand the simplest instructions.