I am constantly amazed by people that say they know about ADHD, then go and deal with that person inappropriately and they wonder why a small situation has turned into a major incident with both parties at loggerheads with each other. We all know how difficult dealing with a person who has ADHD but please try to think how difficult it is for the person with ADHD. You may only have to deal with a situation every now and then, the person with ADHD has to live with it each and every day.
I am not saying that you have to put up with certain behaviours but having the right information on how to support a person with ADHD can go a long way and eliminate misunderstandings , hurt feelings and make for a far more harmonious relationship. Try asking the person the best way to support them , care and understanding can go a long way please remember this.