This disables the main Mission Control screen (⌃↑), but not spaces or the application windows screen (⌃↓).

defaults write com.apple.dock mcx-expose-disabled -bool true
killall Dock

You can disable Exposé and Spaces by removing or disabling Dock. But it also disables full screen windows, the Notification Center sidebar, the application switcher, Launchpad, and Dashboard, and makes the desktop backgrounds gray.

This disables the main Mission Control screen (⌃↑), but not spaces or the application windows screen (⌃↓). It also makes switching to a space with windows for an application stop working.

defaults write com.apple.dock mcx-expose-disabled -bool true
killall Dock

You can disable Exposé and Spaces by removing or disabling Dock. But it also disables full screen windows, the Notification Center sidebar, the application switcher, Launchpad, and Dashboard, and makes the desktop backgrounds gray.