Pardon is a common word clothed in top hat and evening dress at a dress down party. 'Tis as socially unacceptable as buying one's own furniture. When wishing to prompt a rapscallion to repeat a sentence one has missed, there are only two satisfactory options.
What! (The exclamation mark is crucial to us Brits as a way of showing our disdain without "getting into it")
Sorry? (We may be saying it but don't think for a second there is an apology involved, you should be feeling it.)
*brought to you by tongue in cheek productions.