For me, it was the USENIX Security talk on intimate partner surveillance (https://www.usenix.org/conference/usenixsecurity20/presentat...), which introduced me to the field of intimate partner violence (which is typically outside normal threat models) and the crypto keynote on crypto for the people (https://youtu.be/Ygq9ci0GFhA) which similarly introduced me to threats that I hadn't thought about before.