The influence of such things as Kung Fu movies, the explosive popularity of Power Rangers in the nineties, and the prevalence of comic book heroes in our culture have played a significant role in spreading interest in the martial arts. I myself dove head first into martial arts when I was five out of my obsession with the Green Power Ranger. The spectacle and performance aspect of a well choreographed fight scene is a wonderful way to enthrall the imagination of an onlooker, and has been invaluable in making the global martial arts community what it is today.
However, this spectacle breeds the misconception that martial arts are intended for such displays. That everyone who does Kung Fu makes the Bruce Lee noises (spoilers: it's basically just him, with a few exceptions), that we all do back flips and gymnastics moves, or worst of all, that a martial artist can just use their knowledge to look badass on the fly.
With the exception of styles like capoeira, which incorporates gymnastics and acrobatics into their techniques, there is actually very little spectacle involved in pure martial arts. Don't get me wrong, there is a huge benefit in training in gymnastics as a martial artist. They use the same concepts of proper form, full body strength, and precise control, and the balance and understanding of how your body moves and can be moved that gymnasts learn can easily be applied to martial arts. However, there is almost no practical application to excessive leaps, flips, and the like in combat.
In combat, flash means time, and the flashier the technique, the longer it takes to execute. Every moment you take to make a move is a moment you are handing over to your opponent to react. A good analogy is the famous shot from Indiana Jones. He walks up and there's a man doing all of these fancy flourishes with a scimitar. It's five seconds of showmanship. What does Indy do? He shoots the guy. If, instead of doing showy flourishes he had immediately lunged at Indie, our hero wouldn't have had the time to pull his gun and fire. In fact, the original script called for a fancy fight scene, but Ford was sick that day and just look at Spielberg and said "can I just shoot him?" So we instead see Indie go for the quick, clean, and efficient method.
In training, flourishes teach you finer control of your tools, be they weapons or your own body, and are useful in teaching you how to maneuver your tools in whatever manner is necessary. They are overly complicated to make the simple acts easier.
Any experienced martial artist could, if they so chose, choreograph a fight scene or a move sequence to show off and look cool. But that's not really a demonstration of their skill. The better martial artist isn't the one who puts on the best show, but the one who embodies their style's philosophy, has mastered their techniques, and understands when and how to use their skills appropriately.
Many of my martial arts friends don't tell people they practice, especially those who are black belts. It isn't because we aren't proud, but because we understand that what that aspect of our lives means to us is not at all what it means to other people. We could show off that jump 360 round house kick, break boards and cinder blocks, demonstrate fancy locks and throws, but to someone who has dedicated hours upon hours of time perfecting their techniques and training until they were sore and carefully picking apart what they knew to find their weaknesses, it's a very hollow victory to get the momentary adoration of a few bystanders.
If your friend ever tell you they do karate, keep all of this in mind. To them, a challenge to show you something cool will be disappointing. Ask them instead to tell you about the style they do, what kind or training they do, and if they have anything useful they could teach you. I guarantee that they will be thrilled to share it with you. And who knows, that might get you interested in the pursuit as well.