"Something has gone seriously awry":
In his dissent in Kelo (buried on page 14), Justice Thomas may well have written my all-time-favorite line of any constitutional opinion (perhaps, in part, because it does not seem to be written to be famous):
"Something has gone seriously awry with this CourtÂ’'s interpretation of the Constitution."
Had this quote been available at the time, I would have led with it in Restoring the Lost Constitution (which began: "Had judges done their job, this book would not need to be written.") One day, it may be added to such "greatest" lines as "The Fourteenth Amendment does not enact Mr. Herbert Spencer's Social Statics."

To help that along, T-Shirts and mugs should now be forthcoming.

I am enabling comments for your favorite ONE SENTENCE lines from judicial opinions.

Update: IMHO The Kozinski quote posted in the comments by Will Baude is awesome. The quote from Justice Thomas remains my favorite, however, perhaps because it is of such general utility.