Disable proxy server for one apt repository
Just declare in a /etc/apt/apt.conf.d/99proxy file something like this :
Acquire::http::Proxy {
your.local.first.repository DIRECT;
your.second.first.repository DIRECT;
};
DIRECT tells apt to use a direct connection to connect to the repository.
This is just @Cédric Julien's answer with (thanks and) the additional syntax for defaulting to an external proxy:
Acquire::http::Proxy "http://proxy:8080";
Acquire::http::Proxy {
in-house.debian.example.com DIRECT;
no-protocol-colon-or-slashes.example.com DIRECT;
};