Maybe you could turn things around and mildly mess with them a bit when they do this, by saying something like “Hello down there!” I feel like I’d probably do something like that if I were exceptionally tall, heh, but I am an oddball.
I imagine you’re probably the tallest person a lot of folks will ever see, so some surprise is obviously going to happen pretty regularly. I don’t think most people likely mean offense by it – people often don’t know how to respond when something occurs that doesn’t fit into normal routines – it can trip a circuit, of sorts. As for the ones who are genuine assholes? F 'em! You seem like a perfectly nice fellow.
I’m pretty short, 5’6", and I have a friend who’s quite tall, quite a bit over 6’. One time we were at a trade show (we’re in the same industry) and hatched comedic plans – when we saw each other in a pretty crowded exhibit area, I ran up to him, leaped into his arms, and he swung me around a few times. I know we thought it was hilarious! LOL!
I have another quite tall friend/colleague I work with at my own company. Sometimes my dark hair gets a bit shaggy. I can’t remember where the idea came from (might have been his idea?), but somehow one day it came up that it would be a good thing if I climbed onto his back, so we could imitate Hodor and Bran from Game of Thrones. Oh man, hilarity ensued!
Anyway, not trying to make light of the challenges that having a genuine uniqueness can cause. But make sure to remind yourself that your friends don’t give a shit about it, and in many ways, both literally and figuratively I suppose, it will give you the opportunity to experience life from another perspective. This is the bbs for happy mutants after all. 
