Across the hall neighbors...

I've got a friend who has an unusual problem. He gets really worked up because his across the hall neighbor leaves a pair of his shoes in the hall next to his door. It's just an ordinary pair of shoes. I don't think they smell bad or anything; my friend just doesn't like to look at them when he walks by.

Now, I've had neighbors that leave trash in front of their door and I met someone the other day whose neighbor leaves cat food and a smelly pillow outside their door. These things bother me slightly.
But a pair of shoes?
I could probably get past the whole thing if that was all there was to tell. But he got so irritated by the shoes that he actually stole the lace from one of them. Not even a note or a polite confrontation in the hallway, he just steals one of his laces!
I gave him a hard time about it, so he put the lace back beside one of the shoes. The poor guy must not have realized the lace was gone, because the next day the shoes were gone, but the lace was still there.
A few days later another pair of shoes appears outside the neighbor's door and what does my friend do? Swipes another lace.