noun: short for shitty ass; shortened from sass, so as to differentiate if from 'sass' (meaning cool or edgy). Following the UK name for the Special Armed Service (marine commandos) Sas also has connotations of venturing into dangerous places no one else would brave. Someone who does this is a sasser.
verb: to sas - to do someone up the arse, but using their own fecal matter as a lubricant.
That guy is one mother sasser! He sassed my sister thrice. SHe has a real sas, but I think she may have told him it was chocolate.