Another possibility is heckling, not very classy.
Now there is the speechjammer. It still looks a bit awkward, but I think it will develop in a more handy device. For those that think Freedom of Speech is only for their select in-crowd, and not for people with opposing opinions, this can be a solution. For those getting tired of having no arguments anymore, and can only parrot and come up with only nonsense, or getting a embarassed by their double standards, this might be solution.
It uses Delayed Auditory Feedback
In this paper we report on a system, "SpeechJammer", which can be used to disturb people's speech. In general, human speech is jammed by giving back to the speakers their own utterances at a delay of a few hundred milliseconds. This effect can disturb people without any physical discomfort, and disappears immediately by stop speaking. Furthermore, this effect does not involve anyone but the speaker. We utilize this phenomenon and implemented two prototype versions by combining a direction-sensitive microphone and a direction-sensitive speaker, enabling the speech of a specific person to be disturbed. We discuss practical application scenarios of the system, such as facilitating and controlling discussions.
Source: http://arxiv.org/abs/1202.6106