The fact that those same disruptive little shites who ruined everything for others (in my day) are now simply ADHD-sufferers, for whom we should all make allowances.
Worse are the crappy parents - never at fault at all, of course - who hide behind this. Give it a set of initials, and that's fine - nothing to do with us.
I remember an old client complaining that 'our Ryan's been diagnosed with ADHD, so the school will have to deal with it now', as though it completely absolved him of any responsibilities.
Usually, I'd just nod and tell myself that his money was as good as anybody else's, but just the day before my 7-y-o daughter had been cut on her forehead by a pair of scissors thrown by one of these little c@nts, because her teacher was a designated 'special needs' teacher and every time one of them played up, they were sent to join her class, by definition already hyped-up. Ridiculous policy.
I told him what I thought and that he should find another IT support company, because it riled me so much, with the memory of that phone call informing us of what had happened to my little girl still raw. Not very professional, but at least I didn't thump him - because I don't have ADHD, so it would have been my fault.