I would've reacted the same as the OP, except I'd make sure I told the mgr what I thought of his message to me. Ask son to wait a minute and tell the mgr while not in front of son, employees, or public. At the point the mgr may have offered an apology. If he didn't that would be my last visit.

Bad day or not, any store or restaurant manager only exists for the public. He/she has no other audience. If they are jerks for whatever reason the business will be driven away & he'll blame business failure on rising costs, no help, or something other than his disposition.