I don't know why someone would want to be proud to be a Slytherin. You have a high probability of becoming a future ex-con and that house is full of racists.
The houses in general was a bad idea for Hogwarts. That's one thing Voldemort had right. We saw in the books that some teachers played favorites too much when it came to their house. Funny how Ravenclaw is supposed to be the most intellectual house, but all the notable academic wizards and witches that came from the school were Slytherin or Gryffindor.