In Thailand, the feet are considered the dirtiest part of the body and the head the cleanest. One is not supposed to use their feet to pick things up or to expose the bottoms of the feet to another person. This is considered quite rude.
It is also customary in Thailand to take ones shoes off when entering a house, temple, school, etc. For instance, in my apartment building it is quite reasonable to leave your shoes outside in the hallway. Most Thais seem to have slippers that they wear in the house or even at school (we have some Hello Kitty and Minion slippers worn by teachers at my school). Outside of each class and by the downstairs staircase, large piles of shoes are there to greet you 🙂