Well it depends if your really believe in fairies. If you do most people believe fairies to be good
We were planning for a picnic, but the dark clouds seemed like a bad omen.
Here is an example sentence with the word 'omen':An eclipse is often seen as a bad omen back in the ancient times.
A comet was seen
What you are talking about is called Lechuza and it's a bad omen. The two times I have seen Lechuza bad things have happened.
fairies do not exist .the people who say that they have seen fairies have actually seen an illusion .
The word omen is not a bad word
This can be a good or bad omen. If you don't like bees it is a bad omen however if you appreciate their role in nature it can be a good omen.
It's not an omen it is carelessness or bad luck.
There is no such thing as bad fairies. Only good.
In different societies and cultures, bats have been regarded by some as a "good omen" and others as a "bad omen".
It's a death omen
For their dark color and tendency to feast on carrion (especially after battles) crows are generally considered a bad omen