I have yet to see him actually brag...although a few times I have seen him be confused about how others can't do things.
I think that's pretty common.
I believe that talking about how some things are easier to one person than another and that that's a normal difference helps to counter that confusion that many gifted kids experience. Saying something like "So-and-so runs faster (swims better, jumps higher, etc.) than you do, and you read faster than some other people. It's just part of how different people are made differently" helps to make sense of it for them, and you can follow that thread further to help foster patience and understanding of others who don't learn as fast as the child does.
FWIW, I did the same sort of thing with my kids (even when they were quite young) when they asked about physical handicaps, race, etc. Anything they noticed and asked about, basically. It's all just differences. Not better, not worse, just different.
I think if you ignore differences, you seem to kids to be either stupid or a liar. (Or they feel like something is wrong with them for noticing.) That's not good!
OTOH, if you acknowledge differences and even name them and talk about them, but use the conversation about differences as a teachable moment to convey your values--such as that all people have intrinsic worth and that making someone else feel bad is not okay--you encourage them to accept themselves AND to be good people. Both are important, I think.
Just my opinion...
