a strain of herpes that effects a person by making their mouth frequently dry.
tony: goddamnit why is my mouth so frequently dry?
bill: oh it seems that you may have yerpi's
a type of herpes that effects you by making your mouth become dry. This can occur at any moment, and is very frequent.
Andrew: Ever since i had sex with that taiwanese hooker why my mouth has been so dry. it happens very frequently.
bill: O it sounds like you have yerpi!