Abbreviated form for "Greetings and Goodbye". Applicable in situations where speaker does not have time to strike up a conversation with another person, on facebook when someone attempts to talk to another person when he or she is about to log off, or in situations where one is being hounded by a person whose company he or she finds annoying.
Greg was walking down the hallway, late for his next class, when his friend stops to say 'hi". Greg waves and responds "G and G. I gotta get to my classroom!"
by Crawl-lick April 10, 2011