Acronym for 'Friend of No-One'. Usually applies to friendless loners who sit in the corner... and cry.
Person A: That George is such a loner.
Person B: Oh, I know. He's a total FONO.
fake mono. also known as "the kissing disease".
Jennifer: "Yeah, I went to the doctor & she told me i had Mono, but I'm definitely feeling better & its only been three days"
Me: "so you have fake mono?"
Jennifer: "yeah, i have Fono!"