You handle him professionally bearing in mind that customer is King and he/she has a right to be angry when expectations have not been met since they are spending their money on the project. First you apologize for not meeting their expectation then you promise to deliver within the shortest time possible. Then you look at the project and rectify any reasons that led to the shortfall by for example increasing the number of worker in that project and send quality results to the client immediately after they have been QA'd and promise him or her that it won't happen again.