You use the term "slip of the tongue". I think a better term might be "slip of the brain".
How many people think that when someone gets drunk, the truth comes out. Seems like when they sober up and are told what they have said, then they're severely embarrassed and start to make excuses for what was said. I think the severe embarrassment may be enough to change somebody's behavior...either about drinking to excess (or at all), or explore their deepest feelings.