GIGO....I have actually said this, just never used the acronym..
Garbage in, garbage out
GL....Never knew this one was an acronym
GMTA....I have said this..A LOT....but again did not know it could be an acronym
Great Minds Think Alike
GTMI...remove the G and you can guess this one
Giving Too Much Information
GQ no, not the magazine, which was my first thought...