The "Big Lie" is a dead giveaway. It is very telling in and of itself that someone is using a colloquialism like that. More on Jungle words below...

No matter how sophisticated or experienced you may be, it’s impossible to be fully prepared to cope with a Jungle creature who is willing to take it to the limit and resort to The Big Lie. Regardless of what legal tools you may have on your side, never forget Businessworld Jungle Rule No. 1: If you insist on sleeping with big dogs, you’re guaranteed to end up with big fleas.

Contextually, the Big Lie is something that everybody knows is a lie, but it doesn't matter because multiple people are in agreement and nobody would ever admit to it. An excuse is always proffered along the lines of trust, friendship, or professionality. Additionally and very specifically, it refers to a situation where you do have legal recourse, but it would be too untimely and cost prohibitive. The person telling the big lie in this case would have been in bankruptcy, i.e. has nothing to lose.