MARTHA MAD AT GREY'S DOC?

The atmosphere got sooo nasty after "27 Dresses" star KATHERINE HEIGL stuck lovely foot in adorable mouth on MARTHA STEWART's TV show, blurting that the gorgeous china she'd picked out for her recent wedding was...er, NOT one of Martha's designs. OOPS!

The "Grey's Anatomy" hottie burned bright red as ex-jailbird Martha drilled her with killer eyes and said icily: "Oh...you were ordering before our beautiful china had come out." Babbled Heigl: "Uh...I could switch!"

Breathed Martha: "No...you have to get a second set, that's all." After the taping, say insiders, Katherine tried to apologize, but was stunned when Martha coldly cut her off with "Thanks for being on my show!" - then stalked off. (That's Martha "Murda" Stewart.)