Because I can hear people’s shoes flapping everywhere on campus.
I cannot describe how much I hate that “thwack, thwack” sound that comes from people wearing flip-flop type shoes. It’s most annoying in the library, where among the quiet of the stacks, you suddenly hear:
THWACK, THWACK, THWACK, THWACK.
Then someone makes an attempt at a short run/jog to catch up with their friends while wearing them. That’s when you get the staccato thwacking that has a bit of resonance to it.
I hate this type of shoe and the noise they make with a passion.