Bragging

In our text, the author states in the "Working Conditions For Alternate Activities, #6: Never brag about your opportunities to work on the alternate activities." While I agree about this to some extent, I want to pose the question to open a discussion and please feel free to correct me if I am wrong.

Don't we brag about everything to do with sports? If our team beats the other team, we make an announcement to the entire school. If we win the championship, we buy banners and post them for all to see with the child's name & player #. You hear teachers and other students congratulating the team members in the halls etc. When is it okay to brag about being super smart?