From Word-Detective:
Since I have the NSOED open, I might as well quote its definition of "deadpan," which is
"expressionless, impassive, unemotional; detached, impersonal." Although "deadpan" can be
used to mean simply "unemotional," it's most often heard in the context of humor or joke-telling,
where a "deadpan" mock-serious delivery often amplifies the effect of a good joke. Say, for
instance, that I happen upon my brother-in-law tinkering with the engine of his lawnmower. I
stand back with a deadpan air of confidence and announce, "What you need is a henway."
Puzzled, he asks "What's a henway?" I say "About five pounds," and he throws a wrench at me.
All right, so Noel Coward I'm not.