This phrase is the simply and yet very clear warning when you want someone out of your place( or out of your personal space in case ofbr age if u r unlucky). It means: GetTheFuckOut BeforeYouGetΚιlled .
* u r coming home after a great win in ur muay thai match*
- hey Billy why you jumping my fence?
*realization*
-Billy just GTFOBYGK .