Boardgames. Especially big, rules heavy games like Mage Knight and Twilight Imperium. I'll happily spend a day playing a boardgame and my family just don't get it at all.
My family were doing a dog sledding trip and my brother came off and hit his head. We ended up putting him on my sled, with my job being to keep him awake in case he had a concussion. So I asked him to explain the rules to Twilight Imperium to me which, luckily and unluckily, took. Hours.
I've never hated, but been glad for, a game I've never played more...
(but I'm glad that you, and my brother, and other people get so much enjoyment from them!)
It's not a big game, but I fell in love with Nefarious (specifically a translated version) after encountering it in the wild. Fast pace, simultaneous turns, short games, simple rules, no eliminations leading to people waiting for others to finish, and at the same time has some interesting decisions leading to multiple strategies... And then you add two twists every game, changing the rules, meaning you have to adapt your strategies, keeping it fresh.