That really bugs me. Only as an adult you notice things like that i never noticed it when i was younger. I know a few people who do this. Oneday youll bump into them and theyll say hello and maybe a short conversation and the next week youll be across the road and theyll act like they havent seen you and the next time you see them theyll say hello. I think its weird id rather they said heelo or just didnt bother rather than one time teyll speak the next time not. Am i making any sense here?!