This is true!
However, main reason to wear flip flops in the shower is to avoid warts on the bottom of your feet.
Some warts can easily be "burned" (read frozen) off with liquid nitrogen, but if you get a certain type on the bottom of your feet, the ony option is to DAILY slice off the tops of the warts and pluck out the root-like botton fibres with tweezers....then you have to walk around all day.
This is an excrutiating and gross exercise (hasn't happened tome...heard about it though)...wear the flip flops and look like a fuckin' dork...it beats the alternative!