I started watching midway through the second season (sometime after the
Nimoy napkin episode but before (I think) "
Rock Paper Scissors Lizard Spock"). It is not something you have to watch from the start to make sense. If you know (or knew) any super-geeks or nerds you'll probably find it hilarious.
There are a good number of references to what happened in past episodes, this weeks was a good example but it was the season premier; not so many that you feel you missed the humor.