Is it a joke that my classmates call me s .b?

Classmates call you an idiot. If they scold you in front of you and are laughing, there is generally no malice. It should be a joke. But if you are scolded behind your back and more than one classmate calls you SB behind your back, it may be that you have done something really inappropriate to make people laugh. Have a good communication with classmates. Respect is mutual, and students should live in harmony!