This has been one of my fixations for a long time.
My first time seeing a dude's buttcrack was in high school (2007). One of my classmates, "Sam", a handsome white guy, used to wear khaki shorts a lot. We shared some of the same classes too.
One time in particular in social studies, Sam sat diagonal from me, and slumped back in his seat so far that his shorts came way down in the back and exposed a lot of his creamy white asscrack. I don't even think he had any underwear on underneath. Same thing happened when he sat in front of me in science class. Always got me so horned up.