I don't consider a single draw offer to be rude. Only if you do it over and over again, it is.
Offering a draw

If you are in a lost position versus a skilled player, then resign rather than offer draw. It is more respectful.
I would only offer draw if my opponent is in time trouble.
Sometimes I offer a draw in the first few moves of the game because I have to answer the phone.

Against computer 2 in live chess I was up a Queen and offered the computer a draw (because pizza delivery was at my door) and the computer refused.
How rude.
Nice, lol. Once Comp3 drew because of poor queen placement (stalemate).

Against computer 2 in live chess I was up a Queen and offered the computer a draw (because pizza delivery was at my door) and the computer refused.
How rude.
I have all the computers blocked for that reason.

I wouldn't take it if he was ahead and I offered a draw as a joke, I figured no one would do it or take it seriously, I would feel bad if they did accept it.
So I see your point, that makes sense. thanks for the feedback, it helps to learn what is accepted, I have only been playing a few months, and never before online, so what[s accepted isn't clear. It just sort of reminded me of Monty Python's Black Knight in the Holy Grail,
If the game is won this 'tactic' is not gonna work and if ur afraid he could have a chance not to lose the game because of a psychologic effect (i don't even think there is one) than the game is obviously not clearly won...