blow a/the deal
blow a/the deal
To ruin, spoil, or otherwise botch an agreement, often in business dealings. If the boss finds out I was the one who the big deal at the eleventh hour, I'll be fired for sure. You'll blow a deal every now and again. It's extremely disappointing, but it's just part of life in this business.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.