It's quite common for Adults with ADHD to automatically think the worst and jump to the wrong conclusions. Some of it is do to impulsivity and some of it is due to past experiences. When Adults with ADHD have a poor self image we automatically think the worst about ourselves and it's quite often not the case.
So when you are thinking the worst about yourself stop for a few moments to ask yourself if you have all the facts. If you don't then it's probably a good idea to try and get them. As adults with ADHD we beat up ourselves enough for real things and we don't need to beat ourselves up for things that may not even be true.