SO laughs when I cry?

We've been together a year, and he's usually an amazing boyfriend. When I cry for other reasons, he's amazing and helps me through it. But if i cry when we're in an argument, he'll start laughing at me as tears are running down my face, like it's funny to him. I've told him over and over how hurtful it is and he always says that he can't help it or that it's because whatever I'm crying about is "so ridiculous". I'm a sensitive person but how can he look at me crying and have the ability to laugh at me?