I've had a few epigrams that were sticky, most notably "An example would be handy right about now" and "you have to go slow to get fast."
How's this for one:
"Nouns should be like quarks: rarely found in isolation."
I sing today of the noun phrase. When thinking of users, think "overworked accountant," not just accountant. (Hat tip: Jeff Patton). A "neighborhood" should be a "searchable neighborhood."
A bare noun shrieks "unexpressed assumptions."