Oh, yeah, that Holmes Freak case had probably the weirdest/stupidest motives. No motive better defines "overly pretentious fanboy" than that one.
Shame he took his girlfriend down over it too.
There was another one I remember watching that *may* apply to this topic. It was one of the anime-only cases and I don't remember the exact episode number, though. It was a case involving a hairdresser that Ayumi often went to. When Ayumi comes over for a haircut, she and the Boys find that the hairdresser was murdered by a strangling with a wire hanger.
The culprit (who was the hairdresser's former mentor or something) that she and the hairdresser got into an argument, and the hairdresser slapped her. She took it as an ungrateful gesture after mentoring her for so long and strangled her. Guess it was just a spur-of-the-moment thing going on, but it's a bit of an overreaction over getting slapped.