Let's add this to the list of things we shouldn't have needed to tell you: It's a bad idea to slather TOOTHPASTE all over your genitals.
Some people have been using toothpaste as LUBE and posting about their traumatic experiences online, including things like rashes, irritation, and even burns on their junk. So now doctors are warning people NOT to put toothpaste down there.
Source: The Sun