What's "the D"?
The D is an abbreviated term on the internet for dick, used in the context of a woman requesting intercourse.
It has recently become a common reference, as a way of women expressing their need for cock without outright saying it. And has given rise to all kinds of funny T-shirts such as this one:
When you get the time, have a laugh at all of these user submissions:
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Linked page included images of people under 18. Absolutely no minors can be posted or linked.