ADHD is not an excuse to treat others badly. You don’t say if he’s getting treatment for his ADHD, but I suspect not, given what you have shared. Without accepting his diagnosis and treating his ADHD, nothing is likely to change.
Take a look at this article to help determine if all this behavior is related to ADHD, or something else:
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism