Hacker News Reader

Go to Wi-Fi settings and click the "i" beside the problematic network.

You have two options that should solve the problem. Either:

a) Tap "forget this network", or

b) Toggle "auto-join" to off

This is my solution too. I rarely use "public" wifi, but if I do, I ALWAYS turn "auto-join" off.

Also, from time to time, I go in and reset my network settings, which erases any networks I've forgotten to forget.