Name Ambush:
(noun) When an acquaintance you haven't seen for a long time greets you by name but you don't have time to remember their name.

Joe: "Hi, Andy. How have you been?"

Andy: "Er...Hi. Good. How about YOU?"

Sarah: "Andy, you've just been name ambushed."



P.S.
THIS HAPPENS TO ME ALL THE TIME.

(definition found on Urban Dictionary, or here)
(funny picture of Nicole Kidman found here)