Folllow the below steps to deactivate or disable Bluetooth on Ubuntu system startup

Open a Terminal by pressing Alt+Ctrl+T

Run sudo gedit /etc/rc.local and add this before line with exit 0:

rfkill block bluetooth

Save and close the file.

You should still be able to enable Bluetooth through the top bar applet.

This should work for most systems but it looks like there are a few bugs lurking in the kernel's ACPI for Thinkpads. If you're on a Thinkpad, add the following to /etc/rc.local:

sudo gedit /etc/rc.local

paste the following line

echo disable > /proc/acpi/ibm/bluetooth

Save and close the file.

If you have any problem turning on bluetooth and wifi after using this trick, just open the terminal and run the following command to check which device is being blocked:

sudo rfkill list all