In my early 20s, gaggles of teenage girls scared me. If I saw
  three walking the other way (the 12-15 range), I'd cross the
  street.

  Why? Everything and everybody is a toy to them, especially guys.

  Felt very awkward being cornered with the game playing and the
  fake flirting. It wasn't even the least bit flattering because I
  was a toy. I moved on as quickly as possible and kept walking if
  temporarily cornered. Hence: My dislike of humans in groups of
  three. They get... strange. "For where two or three are gathered
  in my name, there am I among them.". Even when I was religious,
  three was the number, not so much two. Man woman child. Man
  woman cat. Cat dog human. cat cat cat. Doesn't matter. Some kind
  of weird inbetween thing happens. Probably related to the "three
  body" problem in gravity.