Had a vertical of like 24 inches, this was a while back though in gym class, like 10 years ago. I thought my vert was pretty average, but I remember seeing a bunch of dudes get up like 18 or 20 inches, only a few nikkas got in the 30's and my homeboy who was dunking with ease and was the same height as me ( 5'10") only had like a 36 inch vert, and I would've sworn that nikka had a 40+ the way he was getting up. we measured our standing verts but I can't remember what it was.
I think sometimes we take for granted what some of these athletes do, finding guys who can jump in the 30's is pretty rare, even if you're in great shape, and there isn't even that many guys in the nba who can get up 40+. So if the average, out of shape guy is telling you he's got a 30+ or even in the high 20's then that nikka is probably lying.