When connecting to a URL via HTTPS and the SSL certificate doesn't match (such as at a paid Wi-Fi hotspot), Safari shows a dialog asking whether the certificate should be accepted. If you accept the certificate, OS X adds an SSL exception and will never ask about that certificate again.
The question is, where is that exception stored? And how can I get rid of it?
Note that this question is essentially the OS X version of “How do you remove SSL certificate exceptions on iOS?”, however the iOS answers make no sense for OS X.