1. Stupid is as stupid does.

2. When a stupid man is doing something he is ashamed of,he always declared that it is his duty. 

3. When stupid man is doing something he is ashamed of, he always declares that it is his duty. 

4. You stupid bugger! You could have run me over!

5. Oh sod off, you stupid git!

6. I can't get this bloody stupid thing to work.

7. That was a stupid thing to say.

8. He's not stupid, just lazy.

9. You can't make me look stupid.

10. I was stupid enough to believe him.

11. It was a stupid thing to do, I admit.

12. He is as stupid as a donkey.

13. I'll never do anything so stupid again.

14. He made her feel insignificant and stupid.

15. He insulted her by calling her a stupid fool.

16. Ha, ha,(sentencedict.com) ha... She's so stupid.

17. She blushed at her stupid mistake.

18. He was not stupid, just lazy.

19. What a stupid thing to do!

20. What stupid idiot left their shoes on the stairs?

21. It was a pretty stupid thing to do.

21. Sentencedict.com is a sentence dictionary, on which you can find excellent sentences for a large number of words.

22. A stupid fellow is difficult to teach.

23. He's not stupid, just ignorant.

24. It was stupid of you to get involved.

25. I'm not so stupid as to believe that.

26. Why grumble at me about your own stupid mistakes?

27. Don't make such stupid mistakes again.

28. I've really been very obtuse and stupid.

29. A blunt knife may be sharpened on a stone, but if a man is stupid there is no help for his stupidity. 

30. The wise are instructed by reason; ordinary minds, by experience; the stupid, by necessity; and brutes, by instinct.