The Inverse Femtobarn!
The "inverse femtobarn" (fb−1) is a measurement of particle collision events per femtobarn. Inverse femtobarns are often quoted as an indication of particle collider effectiveness.A close second was the shed, which is equal to 10−24 barns or 3.86 x 10−58 square miles.
It took Fermilab over a decade to achieve 1 fb−1.
Third place goes to the einstein, which is a mole of photons (6.022 x 1023 photons) .
Honorable mentions go to the henry, zeptoweber, and of course, snap, crackle, and pop.