At the risk of adding to this bad dream of a thread, I thought I'd give my experience of not to interpret too much into a wave or a lack of a wave.
I was driving my 77 911 (one of those despised middies
) and was focusing to my right at approaching cross traffic, more of a peripherial vision look, my head was still straight (had sunglasses on, so you wouldn't know I was looking to my right).
Anyway, at the last minute, I see a bright yellow newer 2003ish turbo passing right by me. The driver is an overweight middle age guy (I'm overweight but not quite middle age
). He is waving to me and smiling, I notice him too late and don't get my hand up, just see him go by. Probably giving him a deadpanned looked w/ my sunglasses on.
Now I feel like the horses a$$, looking like a air-cooled Porsche snob that won't wave at any of those new water cooled Porsche wanna-be's. When really I'll wave to anybody and am usually looking for other Porsches whenever I'm driving.
Who knows what he thought, but I hope an inadvertent missed wave on my part didn't sour him to folks driving older p-cars.
Likewise, if someone in a different model Porsche doesn't wave to me, I don't write off that whole crowd either.
My $0.02