Yes..rude and highly unprofessional....A big bad if he did it in front of the customer and you felt humiliated. If you are ever a boss in the future you'll kinow how NOT to treat an employee. Use this as a lesson. And be grateful you have a job too.
Sadly, it is sometimes part of working life - especially when you have a rotten boss.
He should have actually told the customer that the words were out of order but he would be afraid of losing the customer and so took that person's side rather than yours.
Just keep your head down whilst looking for other jobs and, as soon as you have secured another, let him know why you no longer wish to work for him.
It is rude,but he/she may have been trying to defuse a situation that may have accelerated ,if it happens more often and it worries you,you may need to speak to him/her about it .
What is worse is seeing a boss chew out his employee in front of the customers.
Yes, it was rude of the boss to laugh at either you or the rude customer. He may have laughed because he was embarrassed or to ease up what could have become worse.