Thankyou for asking id have died inside if no one had
So the Piss Ferret is determined all things are awful, miserable, crap, based on bugger all, or their own bias or just their enjoyment of potentially spoiling other peoples fun.
The Shit Weasel however, will find the tiniest negative thing, no matter how good the over all thing, and point it out and harp on about it.
For example, someones wedding day was bloody brilliant, great food, lovely cake, lots of booze, not too much hanging around for guests... but say, the church was a bit chilly... THATS the bit the Shit Weasel will weasel out, and weasel on and on about until thats apparently ALL there was about the day.
My sister is a bit of a Shit Weasel, can't just accept the overall positivity, she has to drag up the slightest negative and draaaaaaaaag it out and do it to death.
So unlike the Piss Ferret, the things the Shit Weasel points out are real BUT... generally insignificant or, if not, you're trying to let them go because they're in the past and can't be changed now, rather than focus on them!