My grandpa is 88 and being mean as can be. Why is he so mean?

It sounds like he may have developed a type of dementia. It could be Alzheimer's or another type. Several types of dementia can change someone's personality. Please have him evaluated. This is vital since your grandma could be at risk. Your grandpa hasn't changed because he wants to - it's his brain. He can't help it. He needs a doctor's help.
Take care,
Carol

Thnx..his memory is very good, he did have a stroke yrs back and has inoperable fluid on his brain. Their living situation has changed also, my aunt thinks he has been like this for yrs we just never saw it because they were at home not living with me.