Firstly, listen to what they have to say! People seldom disrupt with completely inappropriate comments.
If you are aware of the potential for disruption, before the session:
- Talk to the person, and ask them for their cooperation; or at least ask them to share their concerns with you. (You may be able to address some of their concerns from the front of the room, rather than waiting for questions from the floor.)
- Talk to someone else who can influence the person, and ask them to approach the person and talk to them; or sit beside them and temper their approach if necessary; or just ask them to speak up in favour of settling down/ continue as relevant in support of your facilitation.
- Set some ground rules in your introduction that you can refer back to during the session. Such as, give consideration to the views of other; be open-minded; and save issues for discussion after the session if required to stay on-schedule.
- Listen and acknowledge their concern.
- Give equal (or slightly more) eye contact to the other people attending.
- Tell the person you would be happy to talk further with them later, and (not 'but') that you would like to continue.
- Ask them to cooperate or ask them to hold off and let others speak.
- Make a joke of it - not making light of their behaviour, but giving them a message without them needing to lose face.
- Tell them that you appreciate their enthusiasm/good ideas; explain that you need everyone to have a chance to participate; and ask them to hold back and let others make a contribution. (If they do as you ask, make a point of going to them at the end of the session, and telling them that you appreciate their restraint.)
- Ask someone else that they respect to speak to them.
If someone else chooses to confront the behaviour during the session, be careful not to contradict this person if you agree with what they are saying. If you are not careful you might find yourself defending the person who has been irritating you and others, to avoid that person losing face or out of embarrassment.
If you are in dire straits, you might ask the person to leave, or ask someone else to do this. As this is an extreme approach to take, I would recommend against it if there is anything else you can do.
For some more suggestions, you might want to read Dr Neil Flanagan and Jarvis Finger at Just Ask TOM on this topic. For example, they suggest breaking into small group activities to give the person a smaller audience; or a role reversal by inviting the person to argue the other side of the issue for a while.
Good luck with difficult people. It is a truism that they can be our best defenders if we can bring them around.