I suppose it's your own personal choice. I, however, prefer to just finish them off and be done with it.
Is it unpolite to make three queens?

i enjoy getting all the queens i can before mating someone. As lame as it is it kinda satisfies some sexual fantasy for me.
That actually made me laugh audibly.
I'm a one-girl type of guy, but yes, it is impolite. That's why when I play a good friend I try to get 3-4 Queens to rub it in. This can backfire and cause you to prematurely draw, if you know what I mean. We've all been there.
Fewer Queens = less chance of accidental stalemate.

Well there is almost never a reason to get three Queens except to show off and rub it in...at least no reason I can think of off the top of my head. One could probably fabricate a scenario... It would almost always be faster to mate without getting three Queens. Of course, there is a flip side to that coin. Isn't it impolite for the losing player to not resign once you are up a Queen or two?

If you need more queens on the board, that means you are not thinking!
It may also mean you want easy way out. Certainly, making three queens is not rude! You can make as many as you want. The final goal is to win the game then so be it!

It's hard. When I'm excited with three Queens ... throw in a horse and a couple Bishops for some Thorn Birds action ... I can't always look ahead. It's all about instant gratification and I blow it. I get too excited about the impending mate. Tunnel vision. You know the drill.
>> It's not polite to not resign in a completely lost position
Egggsactly. I wish I thought of that.

well...if you just bother to look 1 silly move ahead that wont happen. just 1 move man...you can do that right?
if not then maybe you dont deserve 3 queens.
I know. I can't actually believe how many people think it's a legitimate concern.

In real life, if a man is messing around with two extra Queens, and he doesnt look a move ahead, his wife can suddendly stalemate him.

If a player won't resign in the face of overwhelming odds, I'll subpromote to knights and bishops to show my contempt

well...if you just bother to look 1 silly move ahead that wont happen. just 1 move man...you can do that right?
if not then maybe you dont deserve 3 queens.
I know. I can't actually believe how many people think it's a legitimate concern.
Yeah, like Silman.
I don't find it rude, but they may be able to trick you into stalemating them if you have 3 queens. Two queens, two rooks or rook + queen should be sufficient for two rook mate.
It isn't impolite, unlike Hearthstone BM-ing, but could go badly.

Egggsactly. However, I am sure that if it happened in a GM tourney then it would be considered rude by cognoscenti...kind of subjective though...
Actually I think not resigning is ok. Those who fights for a stalemate to the bitter end I do respect.