There aren't very many places a mutineer could go...
First off, for a combination of practical and logistical reasons, the ISS has never held its original planned crew of 7, and instead has been crewed by 3 people for virtually all of its service life, the exceptions being Shuttle and Soyuz visits, either for crew changes or to install or maintain parts of the station. The upshot is that, while privacy is still at a premium, it is possible, if necessary, for a crewmember to distance themselves from the rest of the crew for a while to cool off.
If an actual FTFO should occur, as a violation of the ISS Code of Conduct, the ISS Commander has the authority, under the ISS Crew Disciplinary Policy, to deal with the situation as he or she sees fit. Certain doors in the ISS can only be opened from one side, so the other two crewmen could, after subduing the mutineer, lock him in the Progress capsule or a similar small, outlying module of the station while a longer-term plan is hashed out with the ground. As far as actually subduing a lone mutineer, the ISS drug cabinet, if it's anything like previous space missions, will have Demerol available, which is one option; another is simple brute force, though a zero-G wrestling match aboard the ISS is likely to damage some very expensive equipment, and there really isn't any good way for any combatant to get the necessary leverage needed for something like a punch, to say nothing of a body slam. As far as we know there are no weapons aboard the station, and it would make little sense to have them; one errant shot could depressurize the entire station.
Further to another question - How is the ISS equipped to deal with the outbreak of a contagion? - I found that the ISS operations guide indicates that "acute psychosis" and "suicidal thoughts or actions", each of which would create a potential situation for mutiny and threat to the entire crew, are considered medical emergencies. For exactly these types of emergencies, the ISS medical locker contains Haldol and Valium in both oral and IM-injectable forms. Procedures further recommend restraining the crewmember by wrapping his extremities with duct tape and/or bungee cords, then stowing the person in their sleeping bag. There are no cases on record of these drugs or procedures ever being needed in orbit, but someone obviously thought ahead and considered the possibility of someone unexpectedly going off the deep end in a closed capsule hundreds of miles from help.
If the entire crew were to mutiny, and attempt to do something that jeopardized the station, Mission Control can lock the crewmembers out of most station systems and run the thing on autopilot. There really isn't anything else to do, until the next Soyuz heads to the station with the crew replacement. That would likely not happen until Mission Control has regained some semblance of control over the crewmembers aboard the station, and that in turn would involve measures up to and including the withholding of critical supplies, such as food and water (and water is used to make oxygen by electrolysis). The ISS crew simply must cooperate with the ground in order to do almost anything of value to the crewmembers or the station.
Overall, the options for dealing with a crazy person aboard the space station are very limited, and for that reason, astronauts are very carefully chosen, and team chemistry monitored closely during training. Dealing with multiple crazy people, however, is rather simple; lock down the station and wait them out. I can't imagine anything approaching a true mutiny by the crew of the ISS ending well for any of them.
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