That would probably be not long after I started playing which was around 2012. My brother and I had a city world going and he had built an underground house on a plain just to the north of my city... well he said it was underground but the timber roof was exposed. I thought I'd help him out this particular time and covered it over with dirt to help it blend in and make it so it was properly underground. He ended up shouting at me because apparently the roof was meant to be exposed, which I argued essentially made it an "in-the-ground" house instead of an underground one.
About a month later it was going well until my brother attempted to build an Ender portal for the first time... inside his house - not such a good idea as his entire house was built with oak planks, a flammable material.
Anyway, while I was working within my city and well away from his house, he set up his ender portal and went to get his tea (I'd already eaten), and when he got back he found a third of his house had burnt down with another chunk on fire. The first thing he did was blame me for setting fire to it, which I hadn't done because again I working on my city to the south. I helped him rebuild his house and he tried to build a portal again... and about an hour later his house was once more on fire ๐คฆโ๏ธ๐
Long story short, I watched him attempt the ender portal elsewhere and it turned out he'd been building it wrong the entire time ๐