Wait, bragged? How did he consider that to be anything worth bragging over?
Back when I was competing in the Derby, the winner, all three years, was the son of the Pack Leader. I guess having the track in your garage enabled you to test various designs, etc.
My father got so pissed, that the 3rd year, he finally intervened and “helped” me with the sleekest, most aero-dynamically designed car, worthy of NASA. Ended up finishing second by the closest of margins.
As the derby coordinator for our pack this year, I highly recommend having a non-scout division so parent/siblings can build their own cars. It really does help (not eliminate) the problem of the dads giving too much help to the boys.
I think I have a pretty good idea for my entry this year. 
Not to toot my own horn (oh, okay, for exactly that reason): here is my entry this year. My son is still working on his.
