Colloquial/slang short form of 'kimochi warui' (unpleasant; gross). Used to express disgust or discomfort; common in casual speech and can be offensive depending on context.
その虫、マジでキモイ！
That bug is seriously gross!
変な話し方する人、ちょっとキモイと思った。
I thought that person's weird way of speaking was a bit creepy.
冗談でもそんなこと言うのはキモイよ。
Even as a joke, saying something like that is gross.
写真を見てみんなで『キモイ〜』って騒いだ。
We looked at the photo and everyone went, 'Gross!'