get down on (someone or something)
To have or express negative or overly critical feelings toward someone or something. I don't know why you get so down on Robert, he's such a nice guy to everyone! Don't get so down on this vacation to your grandparents' farm. I know it's not very exotic, but we'll still have a great time!
get down on someone
in. to be critical of someone; to get on someone’s case. Don’t get down on me. I didn’t do it!