YSK that you can disable Cortana in Windows 10 with a few easy steps...

*warning, modifications to your registry should only be done by an experienced user.

start -> run -> regedt32.exe

Navigate to Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\

create a new key "Windows Search"

go to the "Windows Search" key

create a new D-WORD (32-bit) : "AllowCortana"

make sure it's set to 0. Then reboot!

Voila, no more annoying Cortana.