Cool, so you're looking to 'show' the idea of patriotism instead of just having a 'tell' kind of sentence like 'Mike was a really patriotic person.'
You're definitely on the right track with body language and metaphors, but it can be tough to focus on the techniques before understanding the process of getting there.
In order to showcase a character's attributes, your priority should be believability. That means you can't have a character go out of his way to do something weird (or out-of-character) just in order to set up an idea. So having the radio randomly start playing the national anthem which brings a tear to his eye, or saying something like 'his mind drifted to the time he fought in the Vietnam War and represented his country with pride' sounds really clunky

I'm a fan of the '5 Senses' rule which encourages you to have 'show' sentences that make use of the character's senses. Taste and smell can be kind of tricky, and it's best not to overuse those ones, but you should be able to use sight, sound, and sense quite effectively.
So then there's the question of what patriotism looks, sounds, and feels like. Given I don't know much about your story, this might be a bit challenging, but perhaps you could have your character lament over visual, auditory, or sensory reminders of their passion for their country, like if your character was a soldier (cause that's where my mind goes when contemplating patriotism) perhaps you could have them touching their clothing and remarking that it was so much different to their military uniform. Then you get to construct a metaphor around that, as in, the character's current clothes feel flimsy and threadbare, not like the thick camo khaki of his army days. Gradually, as the story progresses, you can add in more details, like maybe your character tries to do some gardening and gets dirt on his clothes, and then his wife remarks that he should change, which makes him think about how silly it is that in polite society, one should not have a single stain or imperfection, but in order to protect and defend that society, he had to crawl through mud and grit for two whole weeks to the point where he thought he'd never get his fingernails clean.
That's just my train of thought, but see how we can start with a sensory experience and then keep adding details in order to justify the idea we're 'showing?'
Hope that helps; if you let me know the details of your story then I might be able to offer some more specific advice.
Good luck with it all!
