Pools have always been boring actually - I still always liked the choice to have one in my game though. LOL.
I find swimming in the ocean boring too unless it comes with wind sailing, jetskiis, and diving equipment - then I like it.
The most boring thing of all is laying in the sun tanning. I will never for the life of me figure out why anyone like damaging their skin like that - never mind watch a sim do that for hours. To me there is no point but to look 50 when you are 30 years old from doing that kind of thing too much. Never mind the dangers. But really how is that fun and not boring in the sims. You might as well watch a sim take a nap on a couch. Real exciting! NOT.