What's Happening in the Brain
Inappropriate behaviour is a sign of executive dysfunction. Here is another way to think about it. The most primitive parts of our brains are concerned with survival: eating, movement, reproduction, elimination. The more advanced parts of our brains have learned how to over-ride these primitive parts, so that while still getting these jobs done, we can accommodate those base desires to behave well socially with one another. The highest forms of social behaviour are variants of the so-called golden rule - do for other people what you would like to have done for yourself, and don't do to anyone else something you would not like to have done to you.
The inhibitions that we usefully learn so that we can adapt our behaviours can become unlearned if we lose the capacity for inhibition, and so we act on our basic instincts. Much of the inappropriate behaviour of Alzheimer's disease can be understood in this way.