They were making fun of him because he always voted no.
As Ron Paul supporters, we like the fact that he always votes no on unconstitutional legislation. But I don't care to use a term coined by the enemies of our Constitution in order to make fun of him.
Instead, he always votes no because he's Dr. Know (he Knows our Constitution, he Knows the truth, and he Knows how to stand up against corruption).
In a way, now that more people know him better, the term is actually backfiring on them because more and more people are realizing he's been doing the right thing all along, and they want someone to stand up and say no.
Ron Paul's Convention Speech