When a guy lays on his stomach and a girl hovers her pelvic region above his face while giving him really amazing head. When he's about to come, he will tense up and not realizing, will shove his face into her ass. At this point, she will enthusiastically cut the cheese/drop the bomb and clamp her ass down on his face to ensure he gets a good whiff of her stench.
Commonly used as an act of revenge for previous sexual wrong doing.
"Last night, I thought my girlfriend had no hard feelings over the donkey punch I gave her the night before, because she was really going down on me hard, but I was wrong and I only found out when I started to come and totally got caught in an atomic mouse-trap, I've learned my lesson."
When a mans semen is applied by whatever method to his stomach so that his stomach hair becomes pasted to his skin.
My boyfriend Karl didn't warn me he was going to cum and blew a giant load on my hands, so I wiped it all over him and laughed because he had cum stomach... He tried to hug me, but I got away, cum stomach is for boys!