Trust me, I have a few.

I actually fell asleep during my first showing of ESB (take it easy, it was 9:00 and I was 4 years old), so I missed out on a lot of stuff. My dad was VERY interested in the '04 DVD set when it came out. So, I occasionally found him watching both the Bonus Disc and ESB, and I caught a few clips out of context. The main one was in EOD, and showed what I thought was Luke's death. It was just him screaming "No" after the big revelation, but my young mind took it differently.

TPM was one where I also fell asleep, but I did wake up, a couple times. One of the times, I was legitimately frightened by the terrifying Yoda puppet. The second time, I woke up to the lightsaber battle. I was still dazed, so the events of the final battle played differently in my head. I thought that Obi-Wan had used his own lightsaber to cut down Darth Maul, and my mind filled in the gaps by creating a few shots of his lightsaber falling, and then falling the opposite way. It was flawless, until I watched it again. Oops.

Oh, and you wouldn't believe what I thought Biggs and Luke said to each other at the end of the hanger scene.