GAD

In messages, GAD typically implies the person should know the meaning of a certain word just mentioned. For example, if your friend asks what you mean by "facetious," you might reply with "GAD!"

While more common in the 1990s and 2000s when people still owned physical copies of definitions, GAD has since become obscure. Instead, people may send GI or JFGI.

Additionally, if people actually recognize GAD, they may respond poorly since it is somewhat rude and condescending. Therefore, you should probably use it jokingly with people who know you are using it to tease them.