(Serious): Male genital protection for mountain biking/BMX and for common falls
Genital protection is rarely (if ever) used in cycling because it generally means putting some kind of hard surface in play (or excessive padding).  Either of these can easily lead to some very uncomfortable chaffing problems.  For less "pedalcentric" disciplines this might be acceptable (flatland, downhill, etc).  But, for the rest of the market there just isn't a benefit to loss ratio to justify it.

Many other sports have genital protection equipment that is used regularly.  Like winter cyclists who have to use mountaineering equipment to stay warm, you may have to dip into some other sports equipment cache to accomplish / try what you are suggesting.