I like Pook’s response.
For me, its about the location. If I’m hammering it to the station in the morning, on the way to work, I’m not going to bother waving, blowing kisses or screaming hello to everyone I pass who may also happen to be on a bike (whether they are wearing a helmet, riding a BSO or whatever)
BUT, if I’m rattling along a remote path in the Cairngorms, Lakes or wherever I’m much more likely to wave, or heaven forbid, even stop and have a quick natter, exactly as I would if I was out running or walking in the same area.
It’s polite, civilised and costs nothing.