scaredy-cat; easily startled person
Colloquial, often used teasingly or self-deprecatingly for someone who gets frightened easily.
My younger brother is a scaredy-cat; he jumps at the slightest noise.
I'm such a scaredy-cat, so I never watch horror movies.
From the mimetic/onomatopoeic root ビビる (to be startled/frightened) + 屋 (person with a certain trait). The exact origin of ビビる is uncertain, but it is likely sound-symbolic.