She’s a picnic short of a sandwich.
Your guess is as good as mine
I don't give monkey´s
Bite the bullet.
Not my cup of tea
Not what one likes or is interested in.
Decide to do something difficult or unpleasant that one has been putting off or hesitating over.
Used when one doesn't know the solution or answer to a problem instead of admitting
To not care at all about something
To indicate in a humorous way that you think someone is very stupid