I know it's not as expensive as some others here, but a basement window. I was a latchkey kid, and one afternoon I'd come home from school and taken the dog out for a walk. When we got home, some neighborhood kids showed up and we were playing in the backyard with the dog, and I didn't get around to unlocking the house. And then somehow I lost my keys. I knew my folks would be furious with me for goofing off and losing my keys rather than doing my homework, so I was laser focused on getting inside the house. I took a pipe and broke a basement window, planning to climb inside, let the dog in, and then find a way to fix the window without my parents knowing. (I don't remember what I was planning to do about the lost keys.) And of course, the minute I broke the window, they pulled into the driveway and saw what was going on, and I was grounded for like an eon after that. I'm in my 40s and they still bring it up now and then. My dad replaced the windowpane himself but he was too grumpy to show me how, lol.

Overall, it's a pretty stupid story!