I think the worse part of clippy was that it wasn't predictable. I want my tools to be predictable, I want to have complete mental model of what will happen when I do sth. And it should be as small model, as possible.

Clippy appeared at random intervals interrupting me, and almost never were useful. And even if it was - I can only guess what caused it to appear, so I still won't know how to make it do the same thing again. So I couldn't integrate it into my mental model of application.

So it was just very infuriating interruption.

The same problem is with autocorrect. I hate this thing.