Ferengi Rules of Acquisitions...Let's Quote Them.
I'll start this thread with my favorite rule [#76] Quarrk mentioned in the season 2 episode THE HOMECOMING.
#76. Every once in a while declare peace. It confuses the hell out of your enemies.
Doctor Who Episode Time Heist
Doctor: Call me sometime.
Karabraxos: You'll be dead.
Doctor: Yeah, you'll be old. We'll get on famously.