I would actually say that my #1 is when a client (non-programmer) will tell me how easy or difficult it will be to perform the task that they have just assigned

I would actually say that my #1 is when a client (non-programmer) will tell me how easy or difficult it will be to perform the task that they have just assigned me, in an attempt to have their fee waived/lowered. A typical conversation would involve them saying something along the lines of: "I just need you to do this (insert non-trivial task) for me. It's really easy, it should only take you about five minutes."