As a child I used to love tongue twisters. I would scour books (it being the days before the internet) looking for harder and harder ones to master. A simple "she sells sea shells on the seashore" became far too straightforward very quickly however the classic "Peggy Babcock" reeled off three times fast still catches me out every now and then to this day.
However, coming to Japan opened up a whole new world of pain for me. A quick search on Google shows how many different examples there are. Japanese people love tongue twisters. So as you go about your day, try saying "red paper, yellow paper, blue paper" but do it in Japanese. This is still my favourite. Have fun.
Aka-maki-gami, ki-maki-gami, ao-maki-gami