This paper presents a novel ARQ scheme for multiple unicast flows in a multi-user system, which enhances the aggregate throughput efficiency. The core idea is to exploit knowledge of previously overheard packets by unintended users, and perform wise selection and joint encoding of any retransmitted information. Intended users may decode the jointly encoded packet by exploiting the previously overheard packets. It is found that the throughput efficiency in a K-user system approaches, the fairly remarkable result of, unit value when K goes to infinity. Moreover, complexity and overhead of the scheme is studied and a link to (feedback free) network coding is established.