[Winners]

Don't ruin his internet, simply block his mouse or functions like that so using the internet is difficult.

[supreme00.]

if you want to fuck his modem up use a reverse sock5 proxy and log in his modem page and change all things

[Meerkat.]

You could mess with his DNS settings, so he can't go to any website without knowing the IP address.
You could mess with his firewall, so everything is blocked except your RAT.
You could mess with his proxy settings, so every application using the standard proxy settings won't be able to connect.

Etc, etc.

[R3V1V3Dsu]

You could mess with his DNS settings, so he can't go to any website without knowing the IP address.
You could mess with his firewall, so everything is blocked except your RAT.
You could mess with his proxy settings, so every application using the standard proxy settings won't be able to connect.

Etc, etc.

I would also give the same suggestions. I can't believe what I read on thread before reaching your response. These guys...

[Meerkat.]

Thanks everyone.. but unfortunately none of your suggestions were useful.

Lol, it's three perfect solutions to your question. Just because you have no idea how to implement this doesn't make them "not useful".