As a friend, sharing is caring. At the same time, you must understand the unhygienic factors involved in it. The earphone is a foreign substance to the ears, so the ear shall automatically generate wax to protect it from getting damaged. This wax shall get in touch with the earbuds. While you share the same earphones with your friends is considered good, but unhygienic. You may clean the earbuds with a dry towel or a paper napkin before giving it to them. Follow the same process after getting it back too.