To the poster that asked if Disney was even worth it with all the rudeness, I say yes. Sometimes I think half of what equals a rude situation is the reaction to it. If someone leans on your stroller and you snap with something like, "Move or I will move you." or whatever then I blame you as much as I blame the leaner. It's just not necessary.
Don't anyone take that wrong. It's not okay to lean. It's a total safety hazard for a child. Yes, the adult should absolutely know better and should not do it. No argument. But I love the one response given, "Let me move this out of your way." Simple. Effective. Polite.
I think it's taken me a bunch of trips to chill out about the crowds. Our most recent was the week after Christmas and please trust me when I tell you the crowds are never worse. I saw people losing their cool over it each day, yet our family had a fantastic time. Yep, it was ridiculously packed. You bet we waited in some really long lines. With no doubt we all got very tired and from time to time, we froze our rear ends off. But we've all just learned it's easier to adjust than confront because that never makes anyone feel good, me included.
So yes, I'd be displeased someone was leaning on my occupied stroller. But instead of being snappy about correcting it, I'd just correct it. In this situation, specifically, the guy wasn't going to argue with you about how it was actually okay for him to lean on it. And if it did, you'd have my blessing to take it to the next step.
And just for fun, with regard to parades, lines, shows, fireworks and buses, you only have three choices. Refuse to participate because of a safety issue, let someone else ruin your good time or make the best of it. Safety should come first (My two year old was once forced to stand on a bus and I swore I would sooner get off and wait for the next before doing that again.) but other than that, I always choose to make the best of it and enjoy myself.