A phrase used in the Hitchhiker's Guide to the Galaxyseries.
A mild expression of astonishment, similar in meaning to "Well, that's interesting" or "Well DAMN!", but far far more amusing.
X: Hey Y, did you hear?
Y: What?
X: They're actually going to enforce the dress code now.
Y: *pauses* ...well doesn't that just take the biscuit.
Is the pubic hair (carpet) of the person being addressed the same color as the hair on his or her head (the drapes)? Typically asked of redheads, reflecting curiosity whether the hair color is artificial/enhanced or curiosity about natural variability in the hair color.
One of the most tiresome questions we gingersget is "Does the carpet match the drapes?"