being a noob I don't know what the standard behavior in game is for a "non-active" neighbor.

I've progressed to the point where my code is capable of ordering an attack on a neighbor and i'm thinking of taking out this guy next door that does not seem to be "minding the store", --- so to speak.

Is it considered respectful to notify the guy before I clean his clock?  Or is it OK to just go in and take him down?

He seems to be part of some conglomerate.  He has a sign on his house that says so.  Do I need to prepare for some mass attack from his peeps?

You may want to check the League site to see if they're in an alliance. You can use the tampermonkey script to get that info right into the game map. If you attack someone in an active alliance it's not unreasonable to expect their alliance members to attack back.

Outside of that etiquette is more complicated. People who are on slack and talk with each other regularly tend to be more likely to notify each other of attacks, and lots of people have no problem attacking what looks like dead code without giving them notification. 

There is one player in their alliance that seems to be active, the other two seem to be "dead code".

I'll try and contact the one active guy and see how he's doing.

I need GCL to take an enemy controller.  I have none.

I guess I will need to play a bit longer before taking him out.

LOL