How to disable the apt proxy for some repositories

Just edit the /etc/apt/apt.conf file and write in something like this:

Acquire::http::Proxy {

        "http://proxy_user:proxy_password@my.proxy.host:8080"; 

        your.local.first.repository.net DIRECT;
        your.second.first.repository.com DIRECT;
};

DIRECT tells apt to use a direct connection (without proxy).