I always like to throw in a little humor, when the kids are down. I would surely mention that his arm velo must really be improving, keep up the good work.
I would have the focus be 100% on your son, so it doesn't affect him emotionally or on the field. This may sound harsh, but the dad is a grown man. If he can't catch the ball from a 12 YO, he shouldn't be on the field.
Now's the time to protect your kid!!