I have AT LEAST 5 moments.
1: Sapphire version. I had been training my Swampert all day, from level 50 to 99. All I needed was 200 more EXP. Then my brother slapped the Game Boy out of my hand...
2: Silver version. I had a Bayleef. Morty's first trainer had a Gastly. I'll leave it at that.
3: Leaf Green version. I let my brother play it, and I haven't seen it since.
4: Blue version. I caught the glitch Pokemon.
5: ALL versions. I used my Master Ball on a Pokemon I already had, then (out of reflex), saved the game to go eat.