Well, this is quite trivial question but I could not find a satisfactory answer even after trying many search queries both here and on Google.
I want to share my PC with my room-mate. And I don't want him to access ANY network(LAN included).
So, I can create an account for him and block network access for the same.
I would prefer avoiding any third-party tools as far as possible.
It's a simple home PC hooked up to a router for internet. No domain and other stuff.
(Technically, guest account can achieve this. But somehow, the guest account on my PC has network access!)