I've really enjoyed this thread and learned a few new things!
My mistakes:
~Going to DTD on a weekend. We spent over 45 minutes circling the parking lots, looking for any place to park. DH finally had to drop us off at one end and go to the complete opposite end to park. By the time he got there, we had gone to the boys' favorite stores and DH went in Team Mickey (his favorite) and we were ready to go. Weeknights/days only from now on!
~Hurrying up to wait. We got caught in a massive Wishes crowd on our first trip and ended up separating from the crowd at the bag-check and sitting and waiting for over two hours while they dwindled (monorails were sporadic at best and ferries were running slower than normal). Good news for us - when the line got to the bottom of the ramp (as opposed to still backed up into MK) we got up to join it. That was the moment they started redirecting everyone to the resort monorails. Great news for us - we got front of the line, but I can't imagine the frustration of people who had just reached the top of the ramp only to be redirected to the back of the line!
~Riding the monorail when it's crowded - on our second trip we got seats and a family got on and stood with their ponchos and bags hanging in our faces the whole time. Got to our stop and worked our way to the doors - one of the women in the group lunged for our seats, separated my husband and son (who had just turned 5 at the time - actually ran through their hands as if she was playing Red Rover!!) and my DH had to turn around and jump back on to grab him before the doors closed (knocking the witch down in the process, which I wasn't broken up about at all). I had no idea what was happening since older DS and I had gotten off already, we just heard people start yelling at this woman to move and let DH get to his child. I can't imagine the dirty looks she got, but I hope someone chewed her out for me

. My poor son is not a little boy who scares easily, but he was shaking and clinging to my husband's neck by the time they caught up to us. He loves riding the "train" (monorail) but now asks if there are any mean ladies on it

.
And this wasn't my mistake, but I learned from it: DH said he was crossing MK to get FPs at BTMRR while we stayed in Tomorrowland. He got to the Hub and there was a couple having a huge screaming match. He continued on and got FPs and started back toward Tomorrowland - the couple was
still there arguing! This same trip, a meltdown I've witnessed was when we were waiting for ice cream and the couple behind us were having a pleasant conversation that escalated when they couldn't decide whether to go back to the hotel for a break or stay in the park. One wanted to stay and one wanted to go - this escalated more and more until finally the husband said he was leaving and she could do what she wanted.
As a result, DH and I have a standing rule that if either of us makes
one snappy comment, we either take a break, get a drink, get a snack, or go back to the hotel - no way will we be one of the meltdowns! It's a good rule for us - three trips in three years and we've never had a single meltdown between adults or kids!