Jay Tor

Here's some information on testicular cancer, including prevention:
[url="http://www.nlm.nih.gov/medlineplus/testicularcancer.html"]http://www.nlm.nih.gov/medlineplus/testicularcancer.html[/url]

Breast cancer and sleeping with a bra - sounds like an urban myth. Sleeping with a bra may cause abrasions [scrapes] and some minor skin irritation - but cancer, don't think so.

Your parents may just have wanted to make sure you wouldn't touch your privates in public - so they told you to stop the behaviour entirely. Young children can't always draw the line between acceptable or unacceptable public behaviour. [They probably discouraged you from picking your nose - same idea.]