Tetris (Gameboy on Miyoo Mini Plus)
I was on a train once and was finally - FINALLY! - getting close to finishing 150 lines on Mode B. Totally in the zone, for once feeling like there was a direct connection between my brain and the game, all the pieces were landing just right...so after goodness knows how long, I finally did it. I saw the spaceship lift off for the first time, and...I had missed my stop and had to spend the next hour and a half walking to my destination.
Totally worth it.