stands for get a life
The response to somebody who obsesses over something that is insignificant in the eyes of others. Someone who enjoys doing (or speaking of) things that involve no productivity.
Sophie: Thats the third time this week! G A L!
Phrase used by insecure xenophobes as a response to someone with different hobbies, interests or attitudes to themselves. These people often think they have a lot of friends, but usually nobody really cares for them.
Mary: GAL Nick. Be social!