Permanently deletes the given local users and resets the OS X (Yosemite and later) system to an empty state. After running this script, the setup assistant will run again.

reset_system

#!/bin/bash
# Permanently deletes the given users and resets the system to an empty state

# Ensure that it runs as root
if [ "$(id -u)" != "0" ]; then
    echo "${0} must be run as root, or using sudo"
    exit 1
fi

if [ ! "${1}" ]; then
        echo "Usage: $0 <User> [User]..."
        exit 1
fi

function delete_user {
        if [ "${1}" == "none" ]; then return 0; fi
        USR="${1}"
        GUID="$(dscl . -read /Users/${USR} GeneratedUID | cut -d' ' -f2)"
        if [ ! "${GUID}" ]; then
                echo "Could not find user ${USR}"
                return 1
        fi
        echo -n "Deleting user ${USR}..."
        dscl . -delete /Groups/admin GroupMembers ${GUID}       || return $?
        dscl . -delete /Groups/admin GroupMembership ${USR}     || return $?
        dscl . -delete /Users/${USR}                            || return $?
        rm -Rf /Users/${USR}                                    || return $?
        echo "Deleted ${USR}"
        echo ""
}

for i in $@; do delete_user ${i} || exit $?; done

echo -n "Resetting system..."
rm -Rf /Users/.TemporaryItems &>/dev/null
rm -Rf /Library/Caches/* &>/dev/null
rm -Rf /private/var/folders/* &>/dev/null
rm -Rf /private/var/tmp/* &>/dev/null
rm -Rf /var/vm/swapfile* &>/dev/null
find -x / -name .DS_Store -exec rm -f {} \; &>/dev/null
rm -f /var/db/.AppleSetupDone                                   || exit $?

echo "Finished resetting system"
echo ""

echo -n "Shutting down in 5 seconds <ctrl-C to cancel>..."
sleep 5
shutdown -h now

To run (as root):

curl -sSL https://gist.githubusercontent.com/toonetown/8507edf1bb1794943f01bc48a5a6b502/raw | /bin/bash -s -- ${USER}