By Andrew Downie and Drazen Jorgic RIO DE JANEIRO, Aug 8 (Reuters) - Brazilians brought a football fan's raucous attitude to the Rio Games on Monday, wildly cheering their own athletes, booing and mocking opponents -- and creating uncomfortable moments for Olympic athletes unaccustomed to no-holds-barred partisanship. Brazil-Argentina rivalry is more likely to cross the line from teasing to tense, as Argentinian tennis player Juan Martin Del Potro discovered on Monday during a centre court match against Portugal's Joao Sousa at Olympic Park. More...