public toilets ain't a great environment for things like herpes to live in - they need warm, moist environments like the human body, not cold hard surfaces like a toilet. Anything like this would die very, very quickly. You can't catch crabs either. They, again, like a warm environment and lice are not able to adhere to smooth surfaces. Why would a happy crab jump off a nice warm body onto a cold, hard toilet seat? They don't and in the odd case they do, they don't live long at all.