Could have (done):

(1) When you do not really mean what you say:

• I was so tired.  I could have slept for a week.
• When I saw the result I could have wept.( i.e I felt like weeping but I didn’t )
• I was so hungry.  I could have eaten a horse.
• He behaved so stupidly.  I was annoyed terribly.  I could have beaten him.

(2)  Most often we use ‘ Could have (done) ‘ for things which were possible but did not happen or past ability/permission unused.

• Why did you stay at a hotel when you went to Mumbai?  You could have stayed with my brother. (i.e you had the opportunity to stay with him but you didn’t)
• Did you get to the top (of the mountain)?
• We could have done, but we didn’t try.
• Why did you walk?  You could have taken my car.
• He fell of a ladder yesterday but he’s alright, he is lucky.  He could have hurt himself badly.( But fortunately, he didn’t hurt himself)
• The situation was bad but it could have been worse.

(3)  Could have (done) = would have been able to (do)

• Why didn’t you apply for the job?  You could have got it.
• We could have gone away if we had had enough money.
• She couldn’t have gone away because she was ill. (= she wouldn’t have been able to go)
• You did very well to pass the exam.  I am sure I couldn’t have been able to pass it if I had appeared for it.
• I don’t know how you worked so hard to achieve the target.  I couldn’t have done it.