He didn't want to catch typhus or the plague.
The Dem gathering was in SF, at the Moscone Center, IIRC. The city having typhus, etc., problems is the
Land of LA, 400+ miles away. So the joke should have been that
Creepy Joe isn't agile enough to dodge used needles on the streets and sidewalks
. Or maybe that there aren't enough grope-worthy
straight young women and girls in SF,
.