Calvin tells Rusty that because he is an Omega Chi legacy, he is stuck at that fraternity. While it is true that sororities and fraternities give special consideration to legacies, they are not required to give them a bid. Also, just because a bid is given doesn't mean the legacy is required to accept it. If Calvin was given a bid to another fraternity, (due to their rivalry, the Kappa Tau's could have offered him a bid knowing he was an Omega Chi legacy) there is nothing to say that he couldn't accept that bid.