Most cases of ADHD are just excuses for boredom, laziness or the result of terrible parenting.
First of all, I actually am hyperactive and was treated for ADHD growing up. But by no means would I say that I'm incapable of focusing my attention when I want to.
For me, the "hyperactive" part is undeniably true. I love being in motion, moving around, etc. There are some days where I want to do nothing more than just run around aimlessly, climb, or jump. I routinely test my reflexes jumping snow piles, counting steps and distances, and doing generally silly things with the environment while walking around (mostly between classes).
In short: I have sufficient evidence/experience to suggest that "hyperactivity" is real.
It's the "attention deficit disorder" part of ADHD that I have a problem with.
Based on my own experiences, the drug treatments (Ritalin, Clonazapam, Prozac, etc) are largely ineffective and seem to do little other than introduce new problems.
As a comparison, I noticed no change in my bodily behavior/function (apart from the lack of side effects) once I went off the drugs back in 03'. The only thing that I gained from those stupid drugs is that Prozac made a great sleep regulator.
If something interests me, nothing, (no proverbial "passing butterfly") will divert my attention. Yet the condition as described suggests that anyone with it is mentally compelled to divert their attention for even the slightest of causes.
Given the context of my actions, desires, and general mental processes during periods of both boredom and interest, a contradiction arises wherein my alleged "Attention Deficit Disorder".
When I'm bored, I obviously do not want to focus, but I am able to if I want to.
When I'm interested in the subject, nothing compels me to pay attention to anything else (beyond the extraordinary, like a fire alarm or someone making a ruckus).
The only difference between my fidgeting now and when I was in grade school is that I'm more consciously aware of it and much less overtly competitive with my peers (because I'm an adult, duh).
There probably are real cases out there of people who are mentally incapable of focusing their attention on anything for even short periods of time ("chronic distraction" is the best I can describe it), but most of the many, MANY people I've met who claim to have ADHD (Usually ignorantly opening with "I am ADHD", rather than "I have ADHD") do not seem to exhibit any of the usual symptoms.
That is, there is no consistency within these people aside from "I got distracted"; which doesn't say much when it can(and does) happen to everyone.
I'm sure the drug companies that made Ritalin, Prozac, etc loved the 90s though.