Pardon is twee and cheap - you'd ask the Queen for a pardon, no one else can do that. It seems rude to (UC/UMC) people because it sounds as though you are asking someone you've potentially offended to stop being so offended because they are not the Queen.
My mum once had to take a matron aside at drop off for giving me detention for refusing to say pardon and insisting on what. I was a rebel at 6!