A term used to describe someone who is optimistic in such situations where a majority of people (or, just one particular person) do not want to hear optimism because it is unwelcome; such as Monday morning in an office enviorment.
This term can also be used outside "the office" to describe someone who just might be too optimistic.
Person: I hate Monday mornings.
Optimist: Oh, but it's the start of a new week, the beginning of a new day! Isn't it beautiful out?
Person: You're such a Monday Morning Optimist... it's annoying.