Not a watermelon, but I've learned to be very, very picky when I choose a pumpkin, and I never ever bring them in the house after an incident about 18 years ago. They get no further than my front porch.
I got a large pumpkin at a pumpkin patch with the kids. It was too early to carve (maybe 2 weeks before Halloween?), so I set it on the dining room table with some other fall décor. A few days later as I'm walking through the dining room, I notice a "spill" under the table. It was strange because it was directly under the middle of the table, I couldn't figure out how something spilled there and not around the edges... then I realized the spill was directly under the "seam" where you place extra table leaves, and our pumpkin was sitting directly on top of the seam...
I picked up the pumpkin and it was rotting from a hole in the bottom and leaking nastiness plus a few maggots. Shudder. That was horrifying to clean up.... Shudder.
The messiest thing I've ever seen explode in a kitchen was when I was a teen. My mom used to make homemade chicken and noodles in a pressure cooker. The pot exploded (luckily when no one was in the kitchen...) and sprayed the entire kitchen, floor to ceiling, in greasy chicken broth. We scrubbed for hours to get rid of the oily coating.