It's your funeral - When someone gets a bad outcome of something, we say it's his funeral because the reason why the outcome was bad was caused due to him only and no one else. In other words, it means simply to get the bad results of the bad things you have done.
1. You had not proposed her for 4 years, you never told her, and she went away, it's your funeral.
2. I don't know how this happened but I think it is your funeral only.
3. You could have studied, and passed easily, but you took things really lightly, it's your funeral.