Informal

Definition:

To make a major mistake. Completely mismanage or mishandle a situation

Example:

1) Tom screwed up the whole project, and now we're four weeks behind schedule.

Etymology:

This phrase comes from World War II US Army slang.

Definition:

One who makes mistakes regularly; a failure. (Usually written as 'screw-up' when used as a noun.)

Example:

1) Be careful when you're dealing with Charlie -- he's a real screw-up.