I was always told that Gourami's are friendly fish, but then one day 1 of my male Honey dwarfs decided to make a bubble nest. It was quite amusing to watch a little 2cm gourami chasing away any other fish that decided to get near his nest. Even my 12cm silver sharks (bala sharks) were chased away. In a 180L tank with about 20 odd fish, believe me, it was quite a sight to see the tank seperated into 2 distinct sections, the left for the male gourami and his nest and the right with all the other fish.
Moral of the story? Gourami's are timid until they feel like being mean. Then the "teeth" come out and everyone's afraid.