Let's get technical here for a minute, the only reason for doing this (even thinking about doing this) is that hair rubbing between saddle + shorts and skin causes discomfort through friction - amirite? So, the area in question is quite small and there is no need for a Brazilian massacre as long as you 'hit the spot' so to speak. Here's what you do: remove your shorts and spread the saddle with grinding paste (any car parts shop will have it) and go for a short ride, preferable out of sight of anyone with a delicate disposition, when get home you will be sore briefly, three months tops - all the hair will be gone and your bum will be ground to a shiny finish the shape of your saddle as a bonus.