ServicePointManager.ServerCertificateValidationCallback = (sender, cert, chain, errors) => true;

ServicePointManager.ServerCertificateValidationCallback = delegate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors) { return true; };

// 255 characters - lots of code!
ServicePointManager.ServerCertificateValidationCallback =
    new RemoteCertificateValidationCallback(
        delegate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
        {
            return true;
        });