I was going to post this question the other week, you've beaten me to it.
What is the diagonal nod?
With regards to nodding when in cage, yep, been there done it, or when sat at lights and a bike pulls up next to me, I've nodded then (hopefully they've seen the THINK BIKE sticker in the back and don't think I've got a tick LOL)
Yes, have had thoughts of filtering when in the cage, then suddenly realise I can't. Doh! glad we are all as bonkers as eachother!
With regards to waving, I commute every day and see the same riders, if it's been rubbish weather like recently and then we get a fab patch of sun, I'll sometimes wave in the morning because I'm so pleased to be riding in some nice weather so it's more of a big happy (hey, we made it throught the shite weather) wave to my fellow commuters. There are 2 people I see on a regular basis who don't wave, one is on an L Plated custom thing, has been on L Plates since I started riding 3 years ago!
The other is a new rider to the journey and he/she's on a burgman scooter, I've nodded and never got one back so I've stopped.
If you overtake another bike do you nod, stick out a boot or put out a hand to acknowledge them? I usually stick out a hand or boot, often wonder if they think the boot means I'm trying to kick them! ha ha