You been passing the buck. This disgust with mendacity is disgust with yourself. You!—you dug the grave of your friend and kicked him in it!—before you'd face the truth with him!
Daddy delivers his ultimate diagnosis of Brick toward the end of Act II. Brick is disgusted with his own mendacity before the homosexual desire in his friendship with Skipper. He dug his friend's grave rather than face the truth. Thus Daddy calls his son to judgment: "You!" he cries accusingly.
While Daddy's diagnosis rings true, we should note that it is suspiciously familiar. Indeed, it repeats Daddy's own remark to himself in Act II, where he murmurs in disgust over the mendacity in his staying with Big Mama for forty years. Brick himself has echoed Daddy's outburst on mendacity as a feint, as another way of passing the buck. Daddy has interpreted its "hidden truth. It also seems, however, that he has perhaps projected his own disgust with mendacity onto Brick, marking the narcissistic nature of their relationship.