"I thought my meaning was clear enough- I'm sure Draco would be disappointed to know that his wife was unable to conduct herself properly in the company of a...family friend." Snape would never consider letting it slip to Draco that Parvati had been goaded into an argument with him, but there was no reason for her to know that. He was certain that, at least in relation to Draco, Parvati was the stereotypical pureblooded princess- docile and incredibly reluctant to pit her will against her husband's.