She believes herself to be completely unlovable the way she is now, as if she preferred being the way she was, but she also hates the way she was considering herself to have been stupid - so she constantly takes shots at herself in between threats towards others.
Considering she used to be a before her , it's fitting.
The full extent of this isn't explained until her relationship with Pink is revealed.
What are you even saying? Thinking he will betray her as his mother did, she pushes Steven, making him drop the rejuvenator.
During the movie when Steven is about to search for Amethyst, the Spinel offers to come along, and when Steven asks her to stay put, she immediately lashes out.
She can also coil her extended limbs to form a spring with an inflated fist at the end.