Bianca started getting into chess and challenged Joby. Since they just started dating, she was not aware that Joby was once part of his high school's chess club and even joined competitions (and won).
When Joby won he gloated, which made Bianca pissed off and become quiet for the rest of their date (she was mad, but also very embarrassed to admit why she was *that* mad).
Since Joby and Bianca are both competitive with one another, a lot of their fights involve losing a game to the other (Smash Bros, Age of Empires, Bato Bato Pik and etc.)