Someone who initially appears intelligent but is found to act idiotic in the majority of situations.

A Niddy will - act without thinking
Ask the same question more than twice
Not be able to see something directly in front of them
Have a terrible memory
Be extremely clumsy
Overuse telephones
Think that sarcasm is wit

Under no circumstances can a Niddy multitask nor even think and speak at the same time.

Can also be used as an alternative monika for males named 'Christian'.