Students are being obnoxious

Hi! I just went back into the classroom after being an educational administrator for 11 years. I teach 9th graders and 12th graders. The 12th graders seem fine, but the 9th graders are mocking me. A few of the boys are nodding yes rapidly every time they speak- I realize that’s what I do when I listen to the kids’ responses. Because of the work I’ve done in Scholars, it is not bothering me as much as it normally would but it is still bothering me. I find myself being self-conscious and want to address it now (we are 3 days into school) but I’m not sure how to most effectively address it.

I would love to say look you entitled little fuckers, you are hurting my feelings, but I know that won’t go over well. I’m self-conscious as it is and I also feel pressure to do a good job. The school district where I work consists of a lot of wealthy white people. I am brown/Indian. My 12th-grade class is diverse but the 9th-grade class is entitled white kids whose parents have a lot of money, are attorneys, and have a high sense of entitlement themselves. They are the first to call teachers out on ANYTHING in my experience as an administrator. I guess my F is fear coupled with frustration and anger.

C-teaching at a public high school in NJ; kids nodding their heads (in mockery of me)
T- they are such little shits yet I can’t say that
A- stew on it; thinking how wrong it is, not sure how to address it; am self-conscious
R-I’m not fully present or comfortable being myself

How do I address this?