With the rapid advancement of wireless communication technologies, interference has become a key impediment to the improvement of wireless data transmission performance. Traditional interference management (IM) suppresses or adjusts interference at the cost of additional communication resourceswithoutexploiting interference effectively. Especially when the interference is strong, simply eliminating it may be inefficient and costly. Moreover, wirelessly transmitted data is susceptible to threats such as eavesdropping, which also necessitates a thorough investigation. To address these issues cooperatively, we proposeOpportunistic Parasitic Communication with Asymmetric Demodulation(OPC-AD). In particular, we consider the interference experienced by the intended/target communication (i.e., parasitic) receiver (Rx) as the host signal. The target communication constructs a selection signal carrying parasitic indication information based on the data it intends to send and the data decoded by its Rx using asymmetric demodulation from the host signal, and then sends it to its Rx. This signal is used to instruct the parasitic Rx to extract the desired information from the host signal. OPC-AD allows for the exploitation of the interference (i.e., host signal) for data transmission to an interfered Rx. Using AD can also ensure the privacy of the host communication. Since the parasitic communication is concealed within the host signal, eavesdroppers cannot compromise the confidentiality of the parasitic transmission without precisely decoding the selection signal. Furthermore, considering more practical situations, such as non-zero delay/phase difference between the host signal and the selection signal, the implementation of the proposed method under various modulation schemes, and the enhancement of the probability of successful parasitism, we extend the OPC-AD design to cover a broader range of realistic scenarios. Our experimental results validate the applicability of OPC-AD, while our in-depth simulations demonstrate that parasitic communication can effectively thwart eavesdropping and achieve higher spectral efficiency (SE) than other existing IM methods, particularly in strong interference environments.