There is no rudeness in chess -- only rules. As long as you're making legal moves, no one has a right to complain. I've had losing opponents walk away and let their clock run down (as close to rude as you can get) -- but I still offer a handshake - if I see them again. Chess is also psycological -- and if racking up a few queens is intimidating, so be it. As others have already stated, creating your own stalemate is the only potential drawback.
"Rude" is violating touchmove, asking for a take-back, or hoping no one notices that you're castling with a king that has already moved. (Or crying about a 'mouse-slip'.)
You have the right to promote as many pawns as you want into any piece you want to torture your opponent for as long as you want. If he doesn't like it he should resign. It was his fault for playing badly anyways.