I have a few times pointed out to folk that their saddle is to low.
Don't remember any bad reactions - maybe it's the way I made the suggestion - or my inoffensive yellow look.
I did for a while, after some oddball (in my opinion) posts on here think that I should maybe only proffer this suggestion to folks of the same gender in case I was accused of being outrageously patronising but then thought - nah - folks is folks. We's all cyclists.
Only bad reactions I remember are from cyclists I have had words with over close passes, particularly on the inside.
Riding towards Vauxhall in the summer I did catch up at the lights with one person of opposite gender and gently point out that she had passed very close without so much as a bell. She was very nice and said that she had - she rang it for me - we agreed that it was an over-designed pretty useless bell. She said she couldn't really say this publicly though as the boyfriend had bought it for her.
So a nice exchange.
Sad if you can't talk to folk - many exchanges are positive.
Part of the reason I ride a bike is to be in touch with my surrounding world/people.
Oh forgot - I used to ride with my saddle too low - until years ago a polite word from two priests who adopted me for a while on the Dunwich Dynamo.