If you get a pink slip which is clearly out of bounds contact the FAA and file a complaint and request a second ride from a FSDO Inspector.
Technically I think they can repeal a pink slip. Problem is time frame.
Unless you have a FSDO next door and you can do the ride tomorrow.
Anything that you consider unethical behavior by a DPE can be reported and should be reported to the FAA.
They are not GOD and the FAA giveth and the FAA taketh away designations every single week somewhere in the USA.
After enough complaints the FSDO can decide to observe a checkride. Basically sit in on oral and flights.
Or choose to do more of an ‘undercover’ operation and simply observe from a distance and time an oral examination or interview an applicant after the fact.

“ Oh yeah easy ride, we didn’t even do steep turns!”
(Mandatory item)
“Only two questions on the oral!”

Or an 8-hr oral for a Commercial checkride. Unless it’s entirely conducted in Native American Blackfoot sign language that’s BS.

Arrogant or intimidating behavior.
Telling you to fly by their standards or else.
Telling you to use their procedures because they know best.

Here’s one:
Certain model Aztec has battery on the right hand side. This combined with cantankerous IO-540’s can make starting a bit of a black art. So start the RH engine first since it’s a shorter lead to the battery.
So Ace-of-the-base DPE yells at my student for wanting to start the RH engine first as “you should never do that in a Multi, because what if the LH engine catches fire now you can’t get out since the door is on the right blah blah blah”
Throws my guy off his game then decides ( in the airplane) to pink slip him on a question in the oral that “he was weak on”.
As I’m fuming he tells me he can get me right seat time in a local MU2 for some skanky operator that he knows if I send him more applicants. He can get a word in for me. Wink wink
He knows they have just hired a female FO but “you know what happens every month”.
You can’t make this stuff up I swear.
About 12-13 years ago and I’ve never send him a student again...ever.