You should be able to avoid weak/unwanted WI-FI connections by accessing the advanced menu within the WI-FI settings:

Auto Switch Between Wi-Fi & Mobile Data Networks - LG G3

Most phones have this option to avoid unknown WI-FI hotspots,or,at least turn off the notifications for such.

 

Mine doesn't do anything when I turn WiFi on or off except...turn WiFi on or off. What, exactly, is your phone asking you? More specifics will make it easier to figure out what's happening.

 

it might be showing something like 'sign onto wifi network'. i am not sure why but i get that notification when using my home wifi on my G3, it tries acting as if i have to login to use the internet and it won't get online until i click on the notification which just loads the web browser up. after that it works fine. no other device running Android has this issue at home.

There's another pop-up that might be seen, and this also happens when toggling Bluetooth on. it will pop-up a list of known available connections/devices and ask which one you want. you dismiss the notification by either saying 'not now' or cancel it out.

Another is just part of Android, but most often seen on a Samsung device--'Wifi disabled because internet connection is slow' or 'your internet connection is unstable' or 'disabled due to poor signal' and that one can be turned off in settings-->Wifi-->hit three dot button top right-->advanced-->uncheck Avoid Poor Connections.

The last possibility might be when toggling certain location settings such as GPS you get a pop-up about Google using location services, which you hit 'agree' or 'ok' depending on the device. it just alerts you that Google might use your location for things you may or may not like. to disable that you have to go into location settings and uncheck 'allow Google to use location' then when you toggle GPS on the next time it just toggles on and does nothing else.