I don't even think it's poor form to let people know about your accomplishments so they'll listen to you. There's a couple of guys at my club who I wouldn't have thought much of just from interacting with him. The first is a little awkward and goes off on unrelated tangents for a solid hour if you let him. Most avoid him. But I was having an issue with my gasser carb and he casually mentioned a background in racing and lots of experience with those carbs and offered his help. Turns out he used to be not just a racer, but a racing instructor! He's competed with everything from small 2 stroke go carts to sports cars. He even taught a few things to a current Sprint Cup NASCAR driver back when he was a youngster. Needless to say, the guy was able to fix me carburetor and teach me some things about setup and maintenance of these little 2 stroke gasser carbs. Another is also a bit awkward and can't let any conversation go without telling a story about himself. On the surface, you'd think he's just a goofy old man with his Ugly Stick who likes to get away from his wife on the weekends. Yet he competed at the AMA Nats for a long time, placing in the top 10 multiple times. So if I have a flight trimming question or need to work the kinks out of a maneuver, he's the guy I'm going to.
Yes, some perceive listing of your accomplishments as bragging and being full of yourself. Those who feel that way often don't have any accomplishments of their own. But I see nothing wrong with it. If you want people to listen to you, it helps for you to establish your knowledge with them first so they'll actually give you a chance.