The handmade oreo is when in the act of sexual intercourse, the male poops and ejaculates into his hand. He puts the jizz in the middle and sandwiches it with the poop. Thus it resembles and oreo. Then he makes the woman eat it.
"Dude you know that girl I did last night?"
"Yeah what about her?"
"I made her eat a handmade oreo!"
"Awww yah brah."