Woof woof is very similar to grrr
as in it means whoever is on the receiving end of it is looking mighty fine. You are also very likely to get laid a lot if people say woof woof to you. It's probably best used towards men however as you dont want the woman to think you mean she is dog which is completely different
You see Johnny Lee Miller, that fit guy out of Shameless or Freddie Ljungberg looking particularly shaggable simply say without the addition of any other words......
......a deep dirty laugh to follow can add to the impact