Short form for cum goggles, or specifically referring to dark thick rimmed glasses with large frames, such as those often worn by hipsters or blonde girls with large faces.
If questioned by the wearer of CGs on what the acronym stands for, they refer to cool glasses. This results in hilarious moments when they self-refer to their glasses as CGs.
"Your shitty feminist ex had the biggest CGs, did you ever bust your load on them"
"Hey buddy, did you just call my new hip glasses CGs?" "Yeah man, cool glasses!"