They've been known to associate themselves with cheating criminals. Much of the bitterness in this rivalry stems from that era. Barry Bonds beat the stuffing out of the Padres for over a decade, and Padres fans' association with Bonds became infamous when they threw a syringe on the field during one of his visits to Petco Park.
The Giants announcers determined in 2010 that Petco Park is haunted. No one is really sure why they believe this, but it is probably related to the fact in 2009 and 2010 the Padres have owned them there. Attempts to bring the ghosts with the Padres to the Giants home stadium in 2010 seem to be working. The ghosts couldn't do it all, however, and the Padres lost the division title to the Giants on the last day of the season despite the Padres winning the season series.