Or simply switching the "you" and the "not": "Why did you not wait for me?" :) Reporting
You don't need agreement when the auxiliary verb is avere and the pronoun isn't a form of "lo".
Thank you for that. I did not know that it was only forms of "lo" that had to be agreed with.
I found this online:
When the past participle of a verb conjugated with avere is preceded by the third person direct object pronouns lo, la, le, or li, the past participle agrees with the preceding direct object pronoun in gender and number. The past participle may agree with the direct object pronouns mi, ti, ci, and vi when these precede the verb, but the agreement is not mandatory.
Yes. For questions in English, the verb has to come before the subject, so it should be "Why didn't you wait for me?"