When I see foreign movies, often there are scenes where a character lies on the bed with his or her shoes on. I realize that different countries have different customs, but to me, it looks dirty and unmannerly. When I watch TV or a foreign movie, I often see scenes where foreign students leave their outdoor shoes on while having their lessons. I think this looks strange to Japanese because we must change from our shoes into indoor shoes at the entrance hall when we enter a school building. Even teachers must do so. If students' guardians come to school, they must bring their own slippers with them. If they don't, they'll have to walk barefoot on the cold floor.
At university, we can enter the building with our shoes on but when we enter the gymnasium, we must take our shoes off and put on sneakers. Also, when we enter the gymnasium toilet, we must take off our sneakers and put on toilet slippers. In fact, most Japanese have special toilet slippers in their homes separate from their regular slippers. For this reason, stores sell slippers that are for use only in the toilet.