My father with dementia is in assisted living. He is socially withdrawn, gets mean to others and is demanding to move out. How should I handle this?

With "slight dementia" comes a level of 'withdrawing' It seems to me that perhaps he needs to be moved to an area where there is more 'structure' and can interact with others. His anger could be his way of dealing with his loss of control of his 'facilities'

Does the facility have a 'dementia wing'? If they do, perhaps it would be easier for him to move there and see if this helps him.

Again... don't overlook the possiblity that he could have a UTI. For some strange reason, a UTI seems to affect their demeanor quicker than you can imagine.

Does he have any (understanding/informed) friends that can visit with him? Perhaps a visit by his contempory would help him.

Have the doctors been notified of his change in behavior? Meds should be reviewed as well as his fluid intake and food. ALL of these factors can change a person's demeanor.

Can the staff at the assisted living place help to seat residents with one another at meals, to help them engage socially? Maybe you could go to lunch or dinner with your father and attempt to sit at a table with some others and then get to know them along with your father.