In no particular order –

1. Disobey this command

2. What is a question that mentions the word “umbrella” for no apparent reason?

3. I am jealous of the first word of this sentence.

4. What if there were no hypothetical questions?

5. This sentence is a !!! premature punctuator

6. This is not a complete. Sentence. This either.

7. because I didn’t think of a good beginning for it.

8. This sentence refers to all sentences that do not refer to themselves.

9. Be more or less specific.

10. As long as you are not reading me, the fourth word of this sentence has no referent.

11. Thit sentence is not self-referential because “thit” is not a word.

12. I used to think I was indecisive, but now I’m not so sure.

13. If you think this sentence is confusing, just change one pig.

14. The whole point of this sentence is to make clear what the whole point of this sentence is.

And the best one, a pick-up line :

15. If I were to ask you for sex, would your answer be the same as the answer to this question?

– (I heard that a version of this pick-up line was a title of a conference presentation!)