Well, there could be a few different scenarios where a person might want to say that.Originally Posted by english-lover
Say Mr. X bumps into Mr. Y. somewhere in the shopping mall for example. Mr. X owes Mr. Y seven hundred dollars and has been avoiding Mr.Y for quite some time. He never bothered answering the phone from Mr.Y, never responded to his e-mails and simply vanished from the face of the earth for Mr.Y. There has been no rush to pay Mr.Y his $700.
Eventually, there is no escape. Mr.Y is right in front of him saying "Hello Mr.X".... Mr X is confronted right on the spot, turns red and says to himself "Oh no, I am going to kill myself". He knows his goose is cooked.
So in a nutshell, you would say that when there is a lot of awkwardness, embrarrassment, it's too late, you wish you were somewhere else, etc.