In my school we had one guy with aspergers. Which is now under the ASD umbrella on the mild end. It was extremely obvious this kid was not normal.
He went though phases where he would obsess about bizarre things for about 6 months then move on to something else.
He claimed he would meet with GW Bush at his ranch, and occasionally fly to Washington with him (not long after 9-11)
Then he claimed he was an airline pilot, flying around the country on the weekends (Catch Me if You Can came out),
Then he was a psychic and could talk to the dead on demand. We'd ask him to do it every day for months. He'd sit at his desk and go through convulsions telling kids he'd just talked to their dead grandparent. (some psychic show was on TV at the time)
Then he got really really into ringing church bells, then bagpipes and kilts.
He had all the classic signs, physically and socially, mimicking humor in painfully awkward ways. You could tell he was off within a minute of meeting him. If this guy was on the mild end of ASD and 1/42 people have it, you'd think we'd notice more. Either that or the criteria for diagnoses has shifted in the last 20 years.