Some people are jealous. I run into this all the time for the ability to do math in my head (nothing too bad, but even calculating a 15% tip to the penny without a calculator seems to unnerve people), the ease with which I can operate and repair things, and, of course, using chopsticks.
To my mind, showing off is when you compare different types of chopsticks. I have a nice set of tapered hardwood ones that offer better grip than plastic (important when eating Phở) and better dexterity and versatility than the blunt-tipped disposable ones most restaurants use. When I point that out though, I usually get accused of showing off along with the same sort of odd looks normally reserved for Trekkies.
I agree with @The_Idler in that anybody over the age of 10 who is actually impressed leads a dull life, and I am actually disappointed that many people not only lack the skill to use chopsticks, but actually see it as some sort of arcane thing in the same league as, say, Nuclear Physics. Come on, people; it’s just two sticks and a pile of food!