How do you care for your grandfather when he is urinating on the bathroom floor?

This sounds awful- why was he tested for Dementia- and by whom--was he like this when he was younger--
How long has this been occurring--is he mad that his wife is not 100%

I do not know exactly why he was tested but it was order by his primary care physician. According to my grandmother he has always been a pretty mean person. For the better portion of my life he has just been grouchy. But in the past few years he has become increasingly difficult to deal with. I think it is because he cannot do a lot of the things he used to do when he was younger but he doesn't seem to comprehend that that is apart of the aging process. My grandmother does the best that she can she has severe back problems and is a breast cancer survivor. I try to help with what I can but he doesn't even trust me to even help him button a button for whatever reason.

rddaniel13, This must be a very difficult situation for you. Is there a son or grandson that might be able to speak with him. Maybe he does it for attention from you or his wife.

My grandparents have two sons (51 and 60), but when we or anybody else tries to talk to him about anything he either acts like he doesn't hear us or becomes defensive. The situation is becoming more and more toxic and I feel my grandmother is really getting to wit's end.

Sadly you state he has always been a mean person- our behaviors are usually magnified as we age--and this is what you are seeing most likely.
Without some intervention-- his behavior will worsen--sadly-- for some reason he thinks he can do whatever he wants and whomever expense--
Is it possible for a a few people to speak with him--

Does your grandmother qualify for home health care--or some outside help?

@molly1020, I really don't know. My mother and my uncles don't realize how bad the situation is, they just think my grandmother is exaggerating or they're too wrapped up in their own personal lives and careers to care. And as far as HHC I don't think so because my grandmother despite all is still in pretty good health barring the back problems and cancer history. She has full mobility.

1. First it would be useful to know how much of this behavior he can help. That he "passed" a dementia evaluation in the past is not proof that he doesn't have dementia now. How long ago was this testing done? Two months ago? Four years ago? It makes a difference. Has his behavior changed since then? Does he have other "strange" behaviors besides the pee problem? How is his memory? Does he repeat himself a lot? Help Grandmother think through whether another evaluation might be in order.
2. How much of the behavior is deliberate? Have you seen him do it? I've recently read that problems with eyesight and depth perception can contribute to men peeing all over the place. If the toilet is the same light color as the walls and floor it may actually be hard for him to hit the target, and of course he'd rather come across as a mean old goat than to admit he is having that kind of problem. Painting the wall behind the toilet using an in-toilet cleaner that turns the water blue or green may help if this is the problem. (Of course, it won't help if he really is a mean old goat.)
3. Molly's suggestion about bringing in some outside help sounds good. A housekeeper who focusses on the bathroom might be useful! Or a male companion to accompany Gramps to the bathroom.
4. IF he can control his behavior, then some behavior mod techniques may help to retrain him. But that is pretty futile if he is doing this because his brain is defective.

So ... I think the basic first thing is to try to figure out why this is happening. And his primary care doctor may be the place to start.

Grandmother is lucky she has you there to look after her interests.

Good luck!