I'll wave or nod at anyone and as Ken says, scooter riders get so excited if someone riding a real bike waves to them, that you have to be really careful not to wave to them in heavy traffic for fear of them losing their sh1t completely and crashing and drowning in a shallow pool of their own urine.
Larry's right, many BMW riders (the poncey ones in their 2000 dollar BMW branded wet weather suits on their shiny new adventure bikes) only wave at their similarly gayly clad boyfriends, (not that there's anything wrong with that..........) whereas older BMW riders with their knees out of their jeans and jackets older than dirt normally wave to anyone, usually for help...
Most people here are too frightened to wave to a Harley rider just in case he's a member of an outlaw club, in which case he'll probably knock you off your bike, beat you to death with one hand tied behind his back and rape the eye sockets of your bloody corpse on the side of the road, for your insolence. I wave to them because I'm a massive fat bastaard and particularly unattractive, so they just look away, pretending that they're busy reading their text messages, or cleaning their guns.
Italian bike riders don't wave to anyone, not even other Italian bike riders, usually because they've lost all feeling in their extremities due to the vibrations inherent in their flawed design, and the only time their hands leave the bars is to stoop to pick up whatever's just fallen off their bikes, due to manifestly poor quality control. But they look nice.
Similarly, older British bike riders don't wave much, because with all the oil coating their tires and brakes they're too frightened to let go, riding an old Brit bike anytime is like riding on black ice. Riders of modern Brit bikes (mostly Triumphs, new Norton's are still very thin on the ground) usually wave at Jap bike riders just to make them feel good, (especially Jap "Cruiser" riders who are detested by everyone, except scooter riders) and they wave at Harley riders, hoping to be accepted as equals, but are usually rebuffed, or murdered/eye socket raped by 1%'ers who've become confused and mistaken their bikes for "Rice Burners"........
Cafe Racers are probably the worst of the lot, opinionated without any personal experience or knowledge of the subject, apart from what they've read on "Do the Ton" (on your POS "custom" CB350, preferably down a fcuking mineshaft) or seen on Cafe Racer TV (one of the biggest wastes of TV time a thinking human could endure) so they think that any non Cafe/Brat style/Bobber/hamfisted fcukup rider does not deserve the wonderful gift of their limp wristed salute.
Having said that, don't get me started on Indian/Chinese bike riders...........
