What I find is that ADD/ADHD is always used as an excuse for just being a jackass (in the bullshit cases, and I'm pretty sure the cases I've seen are bullshit)
The most irritating part of it is that only immature people even bother bringing it up as an excuse for anything. People who really have it just deal with it, get on with their lives, and will occasionally ask for extra time in an exam or whatever and that's cool. And so, whilst I do understand it is a real condition, it's usually just a misdiagnosed case of parents being doormats that their kids walk all over.
For all intents and purposes I seriously think the number one cause of "ADD/ADHD" (inverted commas because this only refers to the bullshit claims) is a lack of basic discipline. The simple fact is, focus is no longer trained into kids. Mental focus should be trained like athletes training for marathons: Endurance training. As a music student, coming up to exams we were recommended to take 20 minutes a day or every couple of days to write an analysis of a short musical extract without knowing what it was. If we got one we recognized that was just good luck. The following is essentially the script of how to train someone with "ADD/ADHD" into focusing (read: an actual, valid method of revision that should enforced with a bat should the student refuse to cooperate)
Here's a sample of how to do it:
"Oh, I can't focus on anything! Woe is me! Oh well, BLAME IT ON THE ADHD" Yeah? Well sit your ass down and listen to this one minute extract of music, and in 20 minutes I want you to have a paper written for me fully analyzing it. Can't do it? Too fucking bad! Now here's some Haydn. Fuck, You even know the name of the goddamn composer! Now Analyze!. Still nothing? We'll keep going until you can spout the names and eras of all the major composers, what tells you that it's them from just listening to the musical extract, what musical techniques they have used and what these techniques do to the mood of the piece.
Note: I am doing this to make a point, not to say "go beat up your friend who says he's got ADHD, because really he doesn't and really IS just an annoying jackass" ADD/ADHD is a real thing, But it's assholes that abuse its overdiagnosis that irritate everyone and cause threads like this to even exist.