Aren't they just sitting there? Is there any anchorage? It seems like it would be so easy for them to twist.
It can be easy for them to twist - particuarly during sport - and this can be dangerous. That is why it is important to wear appropriate underwear when doing sport (i.e. not boxer shorts) to ensure that they are supported properly. I know of someone who suffered from a twisted testical whilst running a marathon for this reason.
I see. Well lately i've been terrified of torsion (i dont have it) and its causing me to sit differently and walk extremely careful and only sleep on my back and stay still. I thought maybe if i found out they were somehow rotation proof it would calm my nerves.
They won't twist when you are carrying out normal everyday activities, so relax and enjoy yourself.