The Vietnamese phrase "cải mả" literally translates to "grave vegetables," but in a more colloquial sense, it refers to "irregular and stained teeth." It’s an informal expression often used to describe teeth that are discolored, crooked, or generally not well-maintained.
When using "cải mả," keep in mind that it can be seen as a light-hearted joke among friends, but it might offend someone if used in a serious context.