Used by some of Hispanic (Dominican) people as a way of saying good night. When they start learning english to G often is pronounced as ‘goo’ and the 9 is usually just ‘nine’. So G9 is like an abbreviation for Goodnight
the term "gg" is commonly used when someone does something ridiculous stupid, or an unfortunate event has happened.
"g9g" is pronounced "gee gou gee". "gou" is the cantonese slang for "COCK". By adding "gou", it further emphasizes how fucked up the situation is, such as the following:
"mud 9 ye ar lun yeung??"
"diu 9 lei gor chow hai!!"
"on9 9 yakbun jow"
etc....
ridiculously stupid:
"thomas' penis is so small it's like...g9g man"
unfortunate event:
"thomas dfged like 8 times in a row and passed out...g9g lor"