A chart documenting someone who’s obnoxious (or a GG) in great detail. When one looks at said chart the initial reaction is to “gag”. This is also the full word for the abbreviation GG
Thomas: As you can see by this Gallo Gag Chart, the subjects has objectionable taste in clothes and needs grooming.
John: Please don’t make me Gallo Gag . I think it’s time you turned your life around--you need professional help.