What does this mean: 操 One of my chinese friends always writes this on my notebook at University and laughs.

I don't seem to understand what's so funny about it. any explanation would be fantastic.
"操" means "fuck".

It's usage in Chinese is close to fuck in English.

ps:As a Chinese I can understand him , at hometown you rarely have any chance to say those bad language whenever and wherever you want in public because everyone knows what you are saying.