SHE: I dunno, I’ll ask him.

(Calls over the cube wall)

SHE: Greg, is there an apostrophe in “surf’s up”?

ME: Yes, because it stands for “the surf is up.”

SHE: And what about “bottoms up”?

ME: No, because “bottoms” is plural, not a possessive or a contraction.

SHE: (back to the phone) Okay, he says there’s an apostrophe in the first one but not the second....I dunno, I guess because the surf is definitely the surf but with the second there’s just a whole bunch of bottoms.