Meghan McCain went nuclear on Meghan Markle over her "tone deaf" trailer for her upcoming Netflix cooking/lifestyle series, "With Love, Meghan," essentially saying for someone who fled the Royal Family, it's rich she's now acting like an aristocrat!

McCain was reacting to the promo for her new Netflix show, in which Meghan shows off her culinary skills with her smiley friends in a fancy kitchen that screams privilege. Her celeb guests include Mindy Kaling, Roy Choi, Alice Waters and former "Suits" costar Abigail Spencer.

Meghan says ... "There have been 2 terror attacks in 2 days, major wars raging and Americans can't pay for groceries. We are a county in rage, uncertainly and intensity right now." Short story ... she calls Markle's cooking venture "out of touch."

McCain went on to slam Markle for feeding her ego instead of producing a show to help "bring fresh food to food deserts in low income neighborhoods."

And McCain then dropped the mic with this  ... "This is why the world doesn’t like you, nothing else. Just completely and utterly tone deaf to the moment."

Meghan and Harry may have the last laugh ... they're in the middle of a $100 million deal with Netflix, although the buzz is that the streamer hasn't been thrilled with the content M&H are pumping out.