Visited WDW for our first time in August, the week before school started. I live in Florida, so you'd think I would know about August heat. This was in 1996 before the days of even paper fast passes. Stayed at an All Star and took advantage of the 1990s version of EMH - which was one day a week guests staying at a Disney hotel could get in at 8:00AM. Let my then 8 year old daughter convince me that her first ride ever on a coaster and at Disney should be Space Mountain.
MY knowledge of Space Mountain was Disneyland's, with the 2 person car, so I thought OK. I can remember getting to the park around 8:30 (it seemed the bus ride took FOREVER), got in, wandered around finding Space Mountain and standing in line outside in the blazing sun, even at that time of the morning - I believe this was before SM was renovated with the enclosed queue. By the time we got to the load area, I was now freezing cold from sweating in the sun and the air conditioning. And then shocked to see single rider cars. I sat in the front, with my daughter behind me and as soon as the ride started, she was screaming "Mommy, I'm going to fall out" and kept screaming that the ENTIRE ride. Needless to say, it was difficult getting her to ride anything at Disney that left the ground, so no Thunder Mountain or Splash Mountain, Astro Orbiter. Just Dumbo (and it took some convincing to ride Dumbo), People Mover, the old boat ride around Tom Sawyer Island (not the river boat, more like a canoe), a really expensive and horrible lunch (must have been McDonalds, lol). And then it started to pour, we didn't have ponchos or anything (once again, live in Florida, should have known better and brought rain gear). So we headed back to our room, wet, tired, Mom starting a headache, with plans to go back and see the fireworks. But no, we fell asleep, I wandered over to the food court and bought an expensive and not too good pizza (it seemed like the food court was in another county) and stood outside hearing the boom of the fireworks. And did I mention my daughter had a cast on her arm since she broke her wrist a couple weeks before our trip? Which meant no pool time for her. Needless to say, not a good introduction to WDW for either of us. But my daughter got her ears. And we didn't go back for 14 years.
Most recent "I really wish I hadn't done that"? Going to WDW for 4th of July, forgetting (or not even thinking) that this is BRAZILIAN TOUR GROUP SEASON. ARRRRRRGH!!!!