Introduced via a friend. Clubbed together with a whole bunch of pre-teens from my school to raise £5 that we were being charged for a bad photocopy of the Holmes rules (we believed you literally COULD NOT get D&D rules in the UK then; I've since learned that you could, if you looked hard enough.)
None of the above. A friend was in the D&D club in high school, which was led by a teacher. My buddy told me "Mr. Lincoln has a ring that causes diarrhea!" and I had to find out what he was talking about.
Voted 'introduced by a friend,' but as with several people here, it was actually 'introduced by family;' both my parents played and they included me in a family game when I was old enough to join them.