A morning dewey is when you jizz all over your friends face while they are sleeping or are passed out from consuming copious amounts of alcohol.
Asshole #1: "How was your morning sunshine?"
Asshole #2: "Fucking shit. I was super hungover and I woke up with a morning dewey on face. It had dried up and I couldn't fucking open my eyes. It was the worst."
Asshole #1: "Hahaha, I was the one who gave you the morning dewey. I'm so awesome"
Asshole #2: Go fuck yourself.