When a promiscuous female (or homosexual male) has had semen ejaculated into their mouth/vagina/anus so many times by many different partners that the area begins to smell like old sperm.
"Mate I took Scarlet home last night..."

"Ouch! How'd it go?"

"Not good, she had a wicked case of cum hum..."

"Not good then?"

"Oh God no, I thought I was going to throw up on her and end up churning her butter!"
by MattyHavoc December 20, 2011
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When a female (or homosexual male) has had so much sperm ejaculated inside of them (anus, mouth or vagina) that these areas actually smell like old sperm.
"Oh man, I took Scarlet home last night."

"How was it?"

"Terrible, she had a wicked case of cum hum."

"Oh man, that's horrific."

"Tell me about it, I almost threw up."
by MattyHavoc December 20, 2011
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When you surprise a chick ( or dude) with a cum shot to the face and before they can get mad at you, turn around and fart in their face then sprint for the door.
"How'd last night go Ray?"

"Oh Burt, I gave that broad the business and finished her off with the old cum hum"

"Classic Ray"
by HeyBudHowAreYa March 13, 2019
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