People often join #lisp and talk about how they want to get into "functional programming," and that can lead to confusion as people work out exactly what that means and whether you'll get into it if you get into Common Lisp. A similar discussion on comp.lang.lisp led to this from Didier Verna:
The only definition that should stand is: functional = supports functions as first class citizens, as per Christopher Strachey's definition. And support for any paradigm is indeed a continuum.
I also find particularly annoying when people assume that functional = purely functional. That's the kind of vocabulary fuzziness that leads to comments I've heard too often like:
Lisp? Ah yeah, that's this weird functional language with lots of parens...
Lisp? Ah yeah, that's this weird imperative language with lots of parens...