The whambulance is a figurative vehicle that someone may ride in to rescue themselves from their whining.
On multiple occasions, Lars has suggested complete and utter indifference to the idea of someone being offended by the content on the show. He and Joe make virtually no attempt to censor themselves in rendering their opinions. On one episode, Lars suggested that a certain individual who was criticized on said episode can "go ride the whambulance" if he listened to it and got offended. Joe has become fond of this phrasing as well in later episodes.
Ostensibly, this does not include actual righteous indignation, which is anger toward actual injustice in the world. The show does not endorse injustice itself.