The main character was a guy who wanted a girl to be nerdier so he'd have a girlfriend who shared his interests. There was this ring he got her to put on that makes her nerdier, fatter and more socially awkward the longer she wears it. One notable detail I remember is she goes from being named
Nikki to Nikola, after Tesla. The ring has a mind of its own, and actually tries to get away as she keeps it on far longer than expected. It notably gets to the point where even the main character's nerdy friends find her too nerdy. Eventually it essentially maxes out and escapes by transforming into a model and walking away when no one is looking.