In school we got taught that everyone would have STDs and only the bad people do drugs, when you get older you realise that STDs are really rare, but almost everyone does (or has tried) drugs. amirite?

But most of the common ones are far easier to treat than health class warned

Depends on your life style, if you dont sleep around chances are you wont get one.

They are a lot more rare than health class in most schools would have you believe

You are right. According to the CDC, "More than one out of every six people aged 14 to 49 years have genital herpes," for example.
 
https://www.cdc.gov/std/herpes/stdfact-herpes.htm