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When you just can't manage a full spoon of cum. You've wanked that much that your cum is present but almost ghostlike in substance.
"Tom wanked that much in the car on the way home that eventually he only managed a Dust Cum.."

"I came but I don't know where it went....."
"That's what you call Dust Cum Tom."

On the job all night, she bled your snake dry and even when you came in her eye it was just Dust Cum....
by Erica Cantona October 02, 2013