The beard-second comes to mind; the length the average physicist's beard grows in one second, established as 5 nanometers.
The barn, shed, and outhouse are also used by physicists "A barn is a serious unit of area used by nuclear physicists to quantify the scattering cross-section of very small particles, such as atomic nuclei. It is one of the very few units which are accepted to be used with SI units, and one of the most recent units to have been established (cf. the knot and the bar, other non-SI units acceptable in limited circumstances). One barn is equal to 1.0x10^-28 m^2. The name derives from the folk expression "Couldn't hit the broad side of a barn", used by particle accelerator physicists to refer to the difficulty of achieving a collision between particles. The outhouse (1.0^10^-6 barns) and shed (1.0x10^-24 barns) are derived by analogy." (from wiki)
As far as I know, the barn is actually the main unit of measurement used by particle physicists working with atom smashers.
And the bridge is actually 364.4 smoots, plus an ear. I've walked over that bridge many times going to MIT.