"Numb to it" means no longer bothered or disturbed by it. Examples: - It used to really bother me when my sister made fun of me at school, but now I'm numb to it. - For a long time I got nervous every time he threatened me, but now I'm numb to it. Usually when you're numb to something you're referring to a bad or threatening thing. For example, you wouldn't usually say "I used to enjoy the teacher's praise, but now I'm numb to it." Instead, you might say "I used to enjoy his praise, but now it leaves me hollow," or use some other similar expression.

Can also have a sense of "insensitive to it".