Williwaw - a comic reaction displayed by one who sees someone he or she has not seen in years just pop up nonchalantly in close proximity to them. In the comics, this may be illustrated by bugged-out eyes, a slack jaw, and a large exclamation point suspended over the head, with the subject in turn suspended several inches above his or her prior position. In animation, a williwaw can be shown by the subject shooting backwards with the face wobbling uncontrollably, accompanied by the rapid repitition of the titular sound:williwawlillywawillywawlilly. (I'm sure you've seen the Looney Tunes guys do this.) To indicate a williwaw in the real world, the subject may do an impression of one or more of the Three Stooges, grab their phone and start tweeting, or just put a wet finger into a light socket.
...or words to that effect.