Belittling and degrading a person is a toxic person’s forte and their tone of voice is only one tool in their toolbox. Sarcasm can be a fun mode of communication when both parties are engaged, but narcissists use it chronically as a way to manipulate you and degrade you. If you in any way react to it, you must be “too sensitive.”
Forget that the toxic person constantly has temper tantrums every time their big bad ego is faced with realistic feedback – the victim is the hypersensitive one, apparently. So long as you’re treated like a child and constantly challenged for expressing yourself, you’ll start to develop a sense of hypervigilance about voicing your thoughts and opinions without reprimand. This self-censorship enables the abuser to put in less work in silencing you, because you begin to silence yourself.