Eye contact isn't rude behaviour..........dogs make eye contact all the time with each other. What is important is what the eyes are doing and what the rest of the body language is saying.
Soft, relaxed eyes are neither a threat nor a challenge. But if you combine hard, fixed eyes with a stiff body and slow movement that is either a threat or a challenge and all dogs understand that.
With submissive dogs, until they are comfortable with a person, they will not want to make eye contact. But after you have developed a good relationship with them, they will seek the eye contact just as any other dog will.
It is no different with people, have some fun with this one. Go to a public place..... tighten your body by not breathing nice and deep (shallow, rapid or holding your breath will tighten your body) and then harden your eyes (basically glare at someone you don't know). Hold the stare, if they are threatened by it, they will look at you and look away, move away if they can, fidget and be very uncomfortable, but they will continue to glance at you to see if you are still staring. You can make someone leave a room by doing this............
Now a very confident person, will stare back, with that WTF are you looking at expression, they will hold the stare, their body will stiffen...........and who wins or loses is the one who retreats first or looks away and then moves away. Worse case, they come to you and confront you.
You can do the same thing with soft eyes.
If it is someone you know, they may or may not respond unless you make it very extreme. Then they may question you............
It is also the reason why so many herding breeds can get such huge reactions out of other animals including dogs.........plus I think they like the game
Breeds that have a lot of hair over their eyes can have some really negative reactions from other dogs because the other dogs can't read them correctly and an offence is the best defence in that case.