SAGL is an acronym for "Smiling After Getting Laid". This term is used when someone absolutely cannot wipe the grin off their face when coming in after an excellent and sexually successful night out.
Louise - "Yo, Jane you were totally SAGL this morning!"
Jane - "Yah, it was a really good night"
A SAGL is a Self-Appointed-Group-Leader. Someone who decides out of the blue that they are in charge, with little or no support from the rest of the group. They continue on their own direction whether the groups follows or not, believing them to be following.