I got the joke in Ripper's first post
As for his second more serious post... the radio station I listen to airs a condensed version of Leno's monologue from the previous night, and for the most part I can listen to it straight faced. Occasionally I'll crack a grin, but never laugh aloud.
Admittedly, half the blame doesn't fall on him, since the writers make the bad jokes, but half the blame does fall on him because his delivery, for the most part, sucks.