a case of the 'don't know ya's
When someone who you have met on several previous occasions acts like they don't know you when they see you in a different setting.
Susie: Hey, isn't that Joe from shipping who just walked past our table? He didn't even say, "Hello". I just talked to him earlier today!
Jenny: Yeah...he's got a case of the 'Don't Know Ya's.
Jenny: Yeah...he's got a case of the 'Don't Know Ya's.