Credit: https://www.reddit.com/r/sysadmin/comments/6vqpnx/manager_at_a_client_has_been_purchasing/dm28u96/
I, (moron's name), in my authority as (position) of (company), am hereby directing (your name) to do (dumb thing).
I have been advised that (dumb thing) is a Bad Idea, is against industry best practices, and is likely to cause problems including but not limited to (list of problems). If these problems occur, they are likely to harm the business by (list of consequences here). Additionally, doing this could open the business to liability from (customers/vendors/employees/government/other) because (explain).
Understanding the consequences of doing (dumb thing), and knowing that better options are available, I still choose to order (your name) to proceed with (dumb thing) against (his/her) advice. I accept any and all liability that may come from (dumb thing)'s likely consequences, and I agree that (your name) will be held harmless and blameless if/when any negative consequences occur.
Signed, (moron)