If you wear short shorts, you better be sure that you either have no balls (being a woman or an eunuch helps) or that you are wearing some sort of tight, supportive underwear.
Otherwise, especially when you sit down (more so on a floor), your balls may be visibile, hair and all. In some rather unfortunate cases (short and wide shorts) the balls (or even just one, which is more than enough) may slip out, and just hang there.
Consider also the social, bon ton, quandary for the onlooker. There is just no polite way of saying "Erm, old boy, you seem to have your nuts sitting in sunlight. Don't want to get 'em burned, heh ?".
You may say that this is just proof that balls are a poor design
, and I will concur. Nevertheless, it is among our duties
as humans to adapt our habits to our bodies, since doing the reverse can be difficult.
Unless, of course, you cut your balls off.