I said to my girlfriend nothing can ever make you look ugly...
Because you already look ugly.
Alright listen up, buttercup. This "joke" is basically this guy telling his girlfriend that she's already ugly. He's trying to be slick by saying nothing CAN make her look ugly, but then he hits her with the "because you already are." It's an insult disguised as a compliment. It's also just a really lazy attempt at humor. People think it's edgy, but it's just not original.