Great quote. Whoever said, I think he was right.
Ok, you made me look:
“If you can’t explain your physics to a barmaid it is probably not very good physics.”
—As quoted in Journal of Advertising Research (March-April 1998)
Variant: “A theory that you can’t explain to a bartender is probably no damn good.”
—As quoted in The Language of God (2006) by Francis Collins, p.60
I also particularly liked this one:
“All science is either physics or stamp collecting.”
—As quoted in Rutherford at Manchester (1962) by J. B. Birks
Unsourced variant:
“That which is not measurable is not science. That which is not physics is stamp collecting.”
“Physics is the only real science. The rest are just stamp collecting.”
—(Unsourced)
“That which is not measurable is not science.” is also attributed to Lord Kelvin
Guy had a talent for a well turned phrase!