I dunno, there's still power there, like the person feels they have sufficient power to enforce their public "compliment". I bolded the horn thing as when it happens in a car, there's already an extra added power element there, solely from being in a car.
Cars generally have a lot more power over cyclists and peds, and that doesn't just come from being in several tons of metal. Cars can slow down and shout abuse and then speed off again in a way those other road users can't. They've got this loud horn which they can misuse as obnoxiously as they like, they can creep behind or beside you, they can even very physically threaten you off the road or threaten to drag you in. Obviously the majority of car drivers don't do this because they're not wankers, but the medium gives you that potential power. So I think a horn toot is actually quite an aggressive way of showing their "compliment", and I do find it difficult to believe that the tooters don't recognise that.
The other thing that comes to mind is an experience when I was 18 and walking home from a pub shift, and a group of men in their car decided to shout "oi sexy" or something at me. In those days I was more up for making a stand, so I flipped the bird as they went past. The car then stopped and started reversing directly at me with the doors opening. I almost shat myself
Thankfully they were just doing it to fuck with me, and drove off laughing their heads off. But whilst it probably would have been pretty awful had they just been four pedestrians, definitely the addition of the car added to the power.
Rather sadly, it was due to that and a similar incident later that year why I stopped asserting myself in response to these sorts of experiences