I had committed to the customer of the current project I'm working on through email with a copy to my boss that certain activities will be completed by the beginning of next week. My boss stopped by in the afternoon, screamed at me to stop working on my current project and focus on a new requirement for the next two days.
When I told him that I needed to continue work on my current project since I had already committed to the customer he said he would slap me if I did not immediately start working on the new requirement which he wants completed in the next two days.
I am authorised to deal with the customer and give targets directly to the customer regarding when activities can be completed. I work as a computer vision engineer in a startup.
What should my response be? He owns the company where I am working.