I've lived with a few men (not all of whom I had an obligation to like) and they have some pretty strange habits and a lot of them are pretty gross. Over the years I've learned to pick my battles about changing them...gym socks on the kitchen table (gentle nudge), re-wearing dirty jeans (ignore), drinking straight from the jug (click of the tongue).
Recently, we had a bunch of house guests so my husband stopped drinking straight from the jug (because sharing germs with the Mother-in-law is pretty gross even to him). But now it's just the three of us so it's back to the old trick. But not when I'm looking. No clicks if I don't catch him.
So how do I know it's happening? The other day I was pouring milk from jug to cup when I noticed chocolate stains on the rim. It was a little like a little kid with chocolate stains on his mouth saying he didn't get into the cookies.