I can't stand the beach, and hate it with a passion.
First of all, it's the sand. It's nearly impossible to put in your shoes. The sand gets stuck to your feet, and it's impossible to brush it off. It gets on your towel, too. When I was younger, I used to fantasize about paving over the sand with smooth concrete. Now I don't, 'cause that would aggravate too many NTs.
Second, it's the people. If their stuck-up attitudes were radiation, the beach would be Chernobyl.
Third, it's the water. Where I live, you need a wet suit to go swimming in Lake Michigan, except in very late August. Also, there's all that nasty seaweed (or should I say lakeweed?) floating around.
Fourth, it's the sun. Except at really high-end beaches, there is no shade available to get away from the sun. As a result, I often get sunburned, and feel the exhaustion that you normally feel when you spend too much time in the sun.
Fifth, it's the boredom. There is no choice but to either swim or sit in the sun. Neither of those is enjoyable. Imagine dealing with that for hours on end. During the few times I went to the beach with my friends, I looked up a nearby bus route nearby that could "liberate" me.
Despite that, I have absolutely no problems whatsoever with swimming pools and water parks. There are always canopies on the pool deck, reasonably warm water, and things to do besides swimming and sitting in the sun (like water slides and a concession stand). To top that, there is *no* sand whatsover. That alone would make me choose a pool over a beach. People's attitude is still a problem, but it seems a lot more tolerable than at the beach. At the very least, I don't feel the need to look up the nearest bus route when going there with my friends.