If you don't want to be disturbed, don't sign in.....simple as that.
Or if you do have to talk to someone.....do it appearing offline.
Also, as all people use statuses in different ways.....they are kinda loosely interpreted.
Some people are Available/Away/Busy the WHOLE time......so that has devalued statuses.
I'm generally set to whatever is appropriate...but I don't want people talking to me, I don't sign in.....which tbf is never, i like being approchable
it's the same principle as a phone-call......a phonecall is someone basically demanding that you drop whatever you're doing and talk to them.....yet no-one finds a phone-call rude
by being signed in you're giving more of an indication that you want to be talked to than you are by having a phone in your house
yet you'd consider someone calling you out of the blue, demanding your attention, as something normal...positive even......yet someone talking to you while you're busy pisses you off?....maybe look a little closer