How can I disable faces in iPhoto?

You cannot. Sorry. Face detection is automatic.

iPhoto is does not have all options, that the more advanced Aperture has, see: Iphoto 11 -How to turn off faces?

Send a feature request to Apple via http://www.apple.com/feedback/iphoto.html.

Future posts involving iPhoto on your Mac should be posted in the iPhoto communithy under iLife.

OT