There's really no absolute number, but of course you can try making your own list. :) The other issue is how "rude" they are perceived. It can vary depending on the context or region.

It depends just how "rude" you are talking about. The late comedian George Carlin had a classic, funny comedy routine about "Seven Words You Can Never Say on Television." Google search on "carlin seven words" to find a Wikipedia article about them and a YouTube video of Carlin doing this routine. Do not use these words. They are seriously taboo. In the United States you could be fired from a job if you used the wrong one at the wrong time in the wrong place.