The "worst case scenario" is the worst result that could happen in a situation. Use this phrase for talking about the possible negative consequences of something.

In spoken English, people often use "worst case scenario" like it's used in the example above:

Worst case scenario, we'll borrow some money from our savings account.

Worst case scenario, we'll lose maybe 5 or 6 hours of productive time.

But the more formally correct way to use it is this:

The worst case scenario is that we may lose five or six hours of productive time.

People actually often talk about the "worst case scenario" to make something seem safe. If you say that the "worst case scenario" is something that isn't really that bad, then it makes your decisions or actions seem OK. For example, moving back in with your parents isn't too bad, so it makes it seem OK that the speaker lost his job.