A: What did the boss say at this morning’s meeting? Could you tell me over lunch?

B: I couldn’t quite get him, to be honest. It seems that he did his thinking on the hoof.

A: Then, how about just lunch with me?

B: Raincheck. I’ve got a meeting downtown in 20 minutes so I’ll have lunch on the hoof.

Note: The original meaning of this idiom is “alive,” referring to livestock. It is also used as a metaphor for “in an impromptu manner.” The usage is chiefly British.