Tripp’s book is very good, and should probably be paired with Boundaries with Kids by Cloud and Townsend (also Christian). I might actually rank Boundaries first of the two except I haven’t finished it yet. But every parent needs to know the principles in it!
I think this might be helpful. Boundaries with Kids: When to Say Yes, When to Say No, to Help Your Children Gain Control of Their Lives https://www.amazon.com/dp/0310243157/ref=cm_sw_r_cp_api_SGiRBbX91BJ1X
First order of business is ditch the anger and transform it into assertiveness or curiosity. It's an inappropriate reaction if the guy was just appropriately responding to your kids need for attention, and it's a useless reaction if the guy was acting like an asshole and was doing it to be mean.
If you don't know how to ditch the anger yet (it would be a normal reaction for someone who doesn't know how to handle their emotions ) then I'd highly recommend the book “Recovering From Emotionally Immature Parents“. Given that you're on the hook to teach your kid how to handle his emotions when people are rude, this is very important.
After that, teach your kids starting now how to avoid being rude in public when appropriate, and when it's ok to be rude in public because a more polite approach doesn't work. A great book to get started down that path is “Raising Freakishly Well Behaved Kids“, and “Raising Children Compassionately“.
At the end of the day, the best way to deal with rude behavior that's not explicitly harmful is to ignore it. Correcting it with unsolicited advice is rude, which sets a bad example for your kid. Acting angry access butthurt about it demonstrates poor boundaries and emotional immaturity which are also bad examples to your kid.
Your jobs is to teach your kid not to get stressed out by the rudeness of others, access only resort to rudeness themselves when necessary to obtain a larger goal. Learning to fully processes the emotional fall out of incomming rudeness, and then let go of it, is an essential dad skill. Your job is to teach your kids to effectively handle rude behavior from ransoms, not taken out personally, and not reciprocate the rudeness.
You handled rude people as you handle any other teaching moment in there life of an authoratative emotional-coaching dad, with gratitude that you had this opportunity to be a great dad to your kid, and maybe some compassion and empathy for the person who was rude.
All the best!
Boundaries With Kids is fantastic and practical.