Revenge, sweet revenge - at work place
Crafted a letter to a vendor who exhausted everyone's patience by legal issues.
Here it goes, edited for confidentiality sake:

After careful consideration we decided to pass on the opportunity to have you among our preferred providers. We also regret the fact that you won't be among the regular vendors. Since the same questions from you keep coming up again and again, we don't see efficient means of bringing this to closure.

We fully acknowledge you as a credible company with a broad customer base. We'll definitely keep your information on file for future reference should the opportunity in different technology/business space arise.

Sincere regards, --