During the car scene with Winnie, Kevin looks into the camera as part of the joke. It is the only time a character breaks the 4th wall in the series.
Kevin breaking the fourth wall in the car with Winnie, wasn't the only time he does this. The only other time he did this was in series 1.
The title refers to The Hulk, a Marvel Comics superhero created by Stan Lee and Jack Kirby in 1962 who gains his super-strength when his alter ego, Dr. Bruce Banner, becomes angry or frustrated.