This used to happen to me in high school all the time, actually, and was one of the reasons why I only considered small colleges. I didn't want to have to deal with trying to walk somewhere, only to have someone stop directly in front of me, and have me almost crash into them. Unfortunately, it still happens on crowded sidewalks all the time.
This weekend my friend and I were crossing the street with our ice cream when all of a sudden the guy in front of us squats down to tie his shoe. Yes I understand it's important to tie your shoelaces so you don't trip on them and fall flat on your face, but really, in the middle of a busy sidewalk, practically in the crosswalk?! No. We almost tripped on him, and in hindsight I wish I had. Or at least "accidentally" kicked him. Why is it so difficult to move just a few steps over to the side? Oh wait, it's not!