The first time I spawned in Minecraft, I spawned on a Plains biome. Having watched one or two videos, I knew I should get wood. A few minutes later, I had a small, vaguely-sortof-notreally blocked off hole. I saw a Skeleton mob and didn't know about the whole bow-and arrow thing and thought it was a fishing pole. I freaked out when I got damaged although it was nowhere near me. I killed it with a wooden sword (noobiness) and it dropped an arrow.
Cue "Ooohhh!" moment. Yeah.
Oh, and there was that time when I messed up a skin and it totally freaked me out. And Herobrine skin on multiplayer. Obvious story is obvious. Gah.