The "sass" you speak of I would attribute to Mars or Mercury in aspect to Uranus/Jupiter.My sister is sassy. Very. And she also has Mercury/Pluto opposite. But i think her ability to "clap back" is more Mars in Gem in aspect to Uranus.
Pluto in aspect to Merc can suggest one who may unwittingly discover people's secrets or something about themselves.
It could be through overhearing a conversation, reading between the lines of what someone says or knowing which questions to ask in order to get a "required" response.
Pluto works very much on a low key level and is not as brusque,straightforward or as "honest" as Mars. Well not initially.
So a Mercury/Mars person may speak harsh words that are more critical and dissatisfied than anything i.e" your father is a loser who drives a beat down car" etc.
Pluto has a heavier sting and its not so much about speaking harshly. But is more about revealing something inappropriate that was supposed to be a secret i.e." why does your father and our English teacher Mrs Bella spend so many afternoons together?"
The Pluto square individual may be privy to this sensitive(Pluto) information (Merc). But be unable to handle the information with tact(square).
The only way that the above individual learns this painful lesson of discretion and minding ones own business is knowing that a separation between Mrs Bella and her husband is realized because of this rumor.
When this individual becomes conscious of the fact that they were indirectly responsible for spreading the news, they quickly learn that knowledge (Merc) is power (Pluto).
And how certain knowledge that others become aware of, can do MORE harm than what was thought possible(especially when unfounded).
Its the aspect of politicians, people in the secret service, investigative journalism, crime detectives and writers, high officials in the army, psychologists/ psychiatrists, people who work with powerful government elites or anyone who handles very sensitive information that must not land in the wrong hands or become public.
Did I mention that I learned the true identity of my Dad when natal Mercury was conjunct transiting Pluto in 2016?
This aspect is POWERFUL. Big(Pluto) revelations (Merc)