Corriedoo

(n.)
The crucial moment of false recognition in a long passageway encounter. Though both people are perfectly well aware that the other is approaching, they must eventually pretend sudden recognition. They now look up with a glassy smile, as if having spotted each other for the first time, (and are particularly delighted to have done so), shouting out 'Haaaaalllllloooo!' as if to say 'Good grief!! You!! Here!! Of all people! Well I never. Coo Stap me vitals,' etcetera.