It's funny, when people do it I get pissed. Then I step back and think, I've done it, just like I'm sure everyone here has. As long as the person realizes what they did, and move or say sorry, or something to that nature I don't mind at all. It's when they do it, know they got in your way, and just don't care at all that I get mad.
Sometimes we have to put ourselves in others shoes. Thats like one time on the bus a dad had his huge double stroller folded up, and his huge backpack on. Well, he's trying to do things and keeps hitting my mom in the face with the backpack (he's standing, she's sitting). After the 4th time, I finally said something to him, and it wasn't in a nice tone (not like I yelled at him, but it was definitely in an annoyed tone I guess you'd say). Looking back, I wish I wouldn't have, could've probably just let him know what he was doing. He really didn't look like he was having any fun trying to carry all that crap. But at the same time if one person has so much stuff they take up the space of 3/4 people on the bus, maybe they should rent a car and drive, or try to take a little less stuff into the parks.