Ever regret something you learned?

I've tried to mold myself into a modern renaissance man, trying to learn enough about everything to hold a conversation for longer than "Oh, you do that? cool."  I want to know it all, but I know I can't.  Now here's a small list of the stuff I've learned (most of the time the hard way), but never really needed.

1. What's inside a modern golfball.  I've learned this lesson the hard way 2 or 3 times now, and every time it's been the same.  Oh and I've never actually needed the information.
2. Telnet.  Now with the prevalence of http and html I will never ever need to know the divine intricacies of telnet. However it did teach me about IP addresses, which springboarded my knowledge of the internet, ethernet and networking as a whole.
3. FTP commands. It taught me UNIX commands as well, but I just don't use command-line FTP anymore.  With all these great programs like CuteFTP and FileZilla, I don't have to Telnet into a server in Toronto in order to access FTP in order to get a demo disk for a new game which then takes all night to download and doesn't actually work because of noise on the phone line.  Things just don't work that way anymore.
4. AT commands.  Modems are automated pieces of separate hardware now.  They have their own brains and don't need me to post commands to it manually.  In retrospect it was a waste of time to learn these commands.
5. QBASIC.  I will cherish those years I spent learning the logic behind programming, even if it was only BASIC that I learned.  It's taught me many things about programming, ranging from program flow, inheritance, and sub-routines, to global constants, run time variables, and type structures (which started me on the path towards more and more object oriented programming, just like everyone else). unfortunately I now have little use for QBASIC but I don't really regret learning it either since it did start me on course for other languages.
6. how to shave my legs.  I've needed this skill only twice in my life and both times were for a sleep study.
7. how to darn a sock. I know how but that doesn't mean I do it.