It's Grumpy Saturday. If I didn't respond to your email or "friend" request, maybe you fall in one of the following categories.
1. People who have exchanged some email with me (or who once commented on my blog, or were once in the same line at a conference) and send me a Linkedin friend request with the default invite message.
2. People I've never heard from asking to become my friend on Facebook.
3. People who send me a long form letter inviting me to speak at their conference, without any kind of personal note at the top.
4. People who resend that form letter three times.
5. People who get all upset when I respond to the last identical copy of that form letter with "Please stop spamming me."
6. People who send me a long rambling email asking me a Python programming question.
7. People who send me a long rambling email proposing a change to the Python language.
8. People who collect pictures of famous people's desktops.
9. People who send me email asking if they can put their ads on my website.
10. People who create fake blogs with computer-generated pseudo-nonsense text that happens to include my name.