This is a complex question to answer so I will stick to the lighter part for now.
I just got of rehab for alcoholism (I am doing great BTW) and it is funny, that is one of the examples that they gave to lighten things up. They actually did a stand up act in the form of "If you have ever … then you might be an alcoholic. The one about finishing someone elses drink use one of them. Everyone there could relate to that. Not finishing you own drink, well that is so implausible to be ridiculous.
There was another funny one that they gave when someone claimed that they didn’t need to be in rehab because they could quit using willpower. The instructor said, “Ok, let’s ask other people about that”. He asked "Ok, alcoholics, do you remember when you had a couple of drinks at a bar and your buddy came up and asked if he could by you another? Remeber when you used your willpower against him and said: “No thanks, I am all set”.
Normal people wouldn’t get it at all but we all cracked up because that could never happen with an alcoholic.