Fear of rejection probably, but in my case it's always about two outcomes when people start accusing me of something I know it's true:
a) complete silence and just calmly waiting for revenge (where I can justify rejecting them AKA passive-aggressive behavior)
b) focusing attention even more on myself and talking about what happened and how good, correct it actually was to do with flipping the blame onto the victims and proving that blamers were in fact into it and wanted me to do this.