Revenge is Stinky
A stunning revelation has been made about the new drug being used by nobles in Scintilla and, more specifically, linked to the Joyous Choir. It is strongly suspected that the substance is made of people! Psykers, in fact. This leads Dariel to quip that 'a liquified psyker is the best kind of psyker'.
For some reason, Dariel's comment gets the acolytes' own psyker a little agitated, Mordecai not quite appreciating the wit. Indeed, a repetition of the quip, to see if he gets it the second time, only forces the psyker to make his own joke.
Mordecai focusses his psyker powers and causes Dariel to spasm uncontrollably, falling to the floor in an amusing manner and writhing around for a few seconds.
Revenge would be served, if the angry use of his psychic powers didn't backfire on Mordecai. A psychic phenomenon is caused by the concentration of psychic force, causing a noxious stench to manifest. But everyone simply thinks Mordecai pooed himself a little from the strain. Either way, he may think twice before using his powers out of spite.