An opportunistic network is a type of challenged network that has attracted a great deal of attention in recent years. While a number of schemes have been proposed to facilitate data dissemination in opportunistic networks, there is an implicit assumption that each participating peer behaves collaboratively. Consequently, these schemes may be vulnerable if there are uncooperative or malicious peers in the network. In this study, we identify five types of non-collaborative behavior, namely free rider, black hole, supernova, hypernova, and wormhole behavior, in opportunistic networks. We also evaluate the impacts of the five types of behavior on the data transmission performance of three widely used routing schemes. Using simulations as well as real-world traces of network mobility, we show that the data forwarding performance degrades significantly as the number of non-collaborative peers, except worm-holes, increases. Moreover, we find that the three compared routing schemes can benefit from wormhole behavior, especially when the network connectivity is poor and the buffer size is limited.