Help! my cousin was bitten by our dog! is this bad?

Depends: First is the dog's rabies vaccination up to date. ?Could the dog have been exposed to a rabid animal (does the dog show evidence of fighting, etc, )? Otherwise the response depends upon the site of the bite, how much tissue was damaged, is there functional considerations (near the eye or mouth)? Unless trivial, it is best to have it evaluated by your family doc or an er.