of course 是一种粗鲁的回答方法吗？如是，什么回答方法较好？

不是。
它是当然, 自然的意思
eg:Of course he would be ashamed to borrow often.
当然, 常常向人借钱他自己也会惭愧的。

• 
  used to emphasize that what you are saying is true or correct （强调所说的话真实或正确）当然 spoken
  
  
  
  • 
    ‘Don't you like my mother?’ ‘Of course I do!’ “难道你不喜欢我母亲？”“当然喜欢！”
  
  
  • 
    ‘Will you be there?’ ‘Course I will.’ “你要去那里吗？”“当然要去。”
  
  
  
  
  • 
    Variant:
    course informal


• 
  used as a polite way of giving sb permission to do sth （同意某人做某事的客气说法）当然 spoken
  
  
  
  • 
    ‘Can I come, too?’ ‘Course you can.’ “我也可以来吗？”“当然可以。”
  
  
  • 
    ‘Can I have one of those pens?’ ‘Of course─help yourself.’ “我能在那些笔中拿一支吗？”“当然，请自己拿吧。”
  
  
  
  
  • 
    Variant:
    course informal


• 
  used as a polite way of agreeing with what sb has just said （礼貌地同意某人刚说的话）当然 spoken
  
  
  
  • 
    ‘I did all I could to help.’ ‘Of course,’ he murmured gently. “我尽全力帮忙了。”“当然。”他轻声低语道。


• 
  used to show that what you are saying is not surprising or is generally known or accepted （表示所说的事不令人惊讶或具有普遍性）当然，自然
  
  
  
  • 
    Ben, of course, was the last to arrive. 本当然是最后一个到的。
  
  
  • 
    Of course, there are other ways of doing this. 当然还有别的方法做这件事。

• 
  of course
  
  
  
  • 
    You say of course to suggest that something is normal, obvious, or well-known, and should therefore not surprise the person you are talking to.
  
  
  • 
    You use of course as a polite way of giving permission.
  
  
  • 
    You use of course in order to emphasize a statement that you are making, especially when you are agreeing or disagreeing with someone.

不是，其它还有可以用的是：

Sure

Not problem

Okay,

不是粗鲁的说法，只是语气比较重，一般用YES 就可以了