Hi Kath, having a son with ADHD with ODD I am afraid no hints or passing comments tp your friend will be met with your request as it is part of the illness. Direct instructions are usually the best way to go - My son understands yes and no but Maybe is something he cannot get to grips with, and will hound me until I have given him a yes no answer.
Having lived with ADHD/ODD for 16 years nearly now - there is a lot I have had to learn - and they say some people do grow out of it, maybe your understanding of ADHD will help you find an answer to your request there are plenty of websites to get information on.
Good luck I can see the rest of the Forum have put some other ideas for you to try
