How to disable WIFI Auto-connect in Android

While native Android does not have this option, the MIUI ROM , does provide it. The ROM has a setting that can toggle auto connection of remembered networks.

The official MIUI ROM is available here and the unofficial international version can be found here.

No. You cannot do this. The OS keeps track of the networks which are configured in the device. It tries to find those networks and based on the priority driven method, chooses an appropriate network and connects to it as soon as WiFi is turned on. As Arpit suggested, you can forget those networks and OS will remove it's configuration from memory.