I was focused on doing useless things like cracking md5 hashed passwords and didn't really believe you could pay for things with it.
Regret on a different level.
I told my direct manager to mine bitcoin for fun. But he being a nerd for UFOs proposed to use Seti@Home.
This was 2009, months after the official launch.
We had extremely expensive servers with multi-cpu setups continuously running. We could have become easily one of the top miners nodes in the world back then. But instead we helped to proof the lack of alien communication towards the earth.