I think it's all due to the personality, some people are more outgoing than others                                                                                                                                                                              

i (try!) always (TO) nod at others on bikes, or thumbs up if overtaking another on a bike (left hand obv) and do the hand, foot thing when over the water, (as with you sharky, even to plod)  but was amazed when (after a previous day out with same group of friends) one of my friends, friends (you get the picture) took me to task, as i had the stupidity to take my hand (left) off the bars to wave, to said friends, as i continued (making progress) along the dual carageway as they peeled off and i continued. i was traveling in a straight line, and he said it was irrisponsible! (he is an advanced instructor) do centrapiedal forces and gyroscopic effects not apply if you wave?                                                                                                                                                                             

I accidently nodded at a scooter rider yesterday. It was dark and foggy but I still felt like I'd been robbed.                                                                                                                                                                             

oh thats gonna take some getting over,go lie down in a darkened room for a while!                                                                                                                                                                             

I'm thinking of having some sort of collar made that locks when a scooter rider is within 100 metres so I don't do it again.