Protein in milk will coagulate when it meets acid, so it will precipitate, which will hinder the absorption of human body. Similarly, don't eat acidic substances when drinking milk.
Protein in milk is 80% casein. When the pH value of milk is lower than 4.6, a large amount of casein will agglutinate and precipitate, which is difficult to digest and absorb. In severe cases, it may lead to indigestion or diarrhea. Therefore, it is not appropriate to add acidic drinks such as fruit juice to milk, so you can't eat it with vinegar.
Guiding opinions:
Milk and vinegar coagulate together, which is the denaturation of protein, and the precipitation is protein. Protein loses its solubility and physiological activity after denaturation, which is not conducive to the absorption of nutrients, so don't drink it together, otherwise it will waste both milk and vinegar.