A nearly all-purpose reaction for a plethora of situations. Similar to "Oh my gosh" or "good grief" or "wow". It is customary for one utterance to be followed by at least an echo or two.
It was a popular expression in the eighties and seems to be making a comeback, just like disco.
David: "I wonder what would happen if I wrote 'extortion' in the memo field of a check."
Jenny: "Haha! Oh, Pat Sajak."
Kicking someone's pet as you are leaving after having a one night stand. You do this just because. Maybe her dog was in front of the door. Maybe she was terrible in bed. But then again maybe not.
The act of becoming sexually aroused while spinning on an office chair in the center of a circle of naked women while using the penis to slap the posteriors of said women. General practice is that upon stopping of the spin, intercourse is had to the point where the objective woman utters as many vowel sounds as possible.