Wow......your grandma sounds like a piece of work. First of all, about the TV/movie/DVD-related problems, I'd suggest writing out instructions on how to use the VCR and DVD player. I did that for my roommates, although they don't watch a lot of movies, because my VCR and DVD player are a bit quirky, and without instructions, they can be really hard to get going. Second, do you have any videos or DVD's of old musicals? I have several, I have "The Sound of Music," "My Fair Lady," "Fiddler on the Roof" and "Annie" on video, all inherited from my maternal grandparents.....they still play and everything, videos are incredibly resilient. Anyway, those kinds of movies are perfect, they're light-hearted, funny, and completely non-offensive. Most older people either enjoy them, or fall asleep in the middle of them, at which point you can take the movie out and watch something that you like better.
As for the other unreasonableness.....I find humour works well. For example, if your grandma complains that wearing shorts and a T-shirt and flip-flops to a car wash is "inappropriate," you could say something like, "Well, gee, Grandma, I was going to wear a snowsuit, but I figured that this would give me a little less heat stroke, so that'd save Mr. Co-ordinator all the hassle of calling an ambulance."; or "Seat belts? Well, gee, Grandma, way to take the fun out of that one!!! Randomboy was just going to have me surf on the hood of his car, since his motorcycle's in the shop right now. It's really a drag for him, the other Underworld's Ethereal Beings have been really teasing him lately, he just can't do the whole bad-bacon-fed knave thing as convincingly with his mother's station wagon with the 'My Son Randomboy is an Honour Student at Blahblah Collegiate' bumper sticker." If that doesn't work, or if she gets uppity with you for being "rude" or "insolent," then I'd just ignore it. I do that all the time with my mom, she'll buy me clothes, or approve of clothes that I buy for myself, and even say she likes them, and then later, when she sees me wearing them, she'll say they're inappropriate--too short, too tight, too loose, ANYTHING. I just don't listen, I mean, I'm 22, I know perfectly well how to dress myself, and she can just go fry ice. Seriously, I think the best option here would be either to stay at a friend's house overnight, or lobby to be allowed to be left alone completely. I know I'd prefer the second option, because I've lived by myself before, but that's not for everyone. As for your grandmother wanting to spend time with you, well, this is going to sound unpopular, but, well.....if she's going to treat you that way, then.....tough. My mom always told me "if you want to be liked, then be likeable," and I don't see how that should be any different, whether you're seven, or seventeen, or seventy years old.