在什么情况下可以使用这个句子？----这个提问本身就有问题。

老虎屁股摸不得，在日常会话里根本不会用到。更多的是在叙述事情（文章）里使用。意思是说对方很可怕，不要惹他生气的意思。

When you are describing a person who thinks he is so great like a tiger, and no one can criticize him. For example， 虽然他是老板，但是也不能老虎的屁股摸不得，有意见就要提出来。Although he is the boss, we can't think 老虎的屁股摸不得, if anyone has suggestions, he/she should speak out.