[OJFord]

I had a flatmate with this at university. On campus he'd totally blank me (different departments), like I'd left something awful in the sink. At home Hey y'alright how's it going like nothing had happened. Bit weird, but you get used to it.

(Basically I just learnt to ignore him out of context too. It was only politeness that would otherwise incline me to acknowledge someone like that, so if they don't recognise me that just doesn't really apply, no need.)