Dean likes boobs.
This is just a fact of life: Dean likes perky boobs on pretty women. Loves them. You can ask John (who tore 13-year-old Dean a new one after he found a crumpled Busty Asian Beauties hidden under the backseat of the Impala) or Sam (who’s had to put up with his brother’s womanising ways most of his life, poor kid).
Women have soft curves and long swishy hair, delicate hands and slender legs, perfect lips and smokey eyes and painted nails, and they always smell nice, like fruity shampoo and elegant perfumes. Women whisper filthy things in his ear, their voices smooth and hushed. And all of it turns Dean on. Big time.
So yeah, Dean likes the ladies. This is an established certitude.
But what it doesn’t explain is why, for the love of God, he can’t stop thinking about kissing Cas senseless.