I am always polite.
Nearly 34 years ago I met SIL1 and SIL2 for lunch the week before my wedding. SIL actually told me that I should think carefully about marrying her brother because he was a capitalist bastard.
Whenever I have met her, she has played the world's noisiest violin about how little they have, blah, blah. How tired she is, blah, blah. She's poor because she and her partner are work avoidant - they are creative and it's just too boring for them. He never visits her family because he is addicted to weed and he wouldn'tbe able to smoke it.
When she had one small son, we took them away for the w/e. She watched while he battered my 16 month old, she watched while he threw rocks at other children, she watched whilst he tried to wreck a holiday lodge. She lay on her back reading while dh and I cooked, washed up, supervised children, having prepped a birthday tea for her son and bought him a cake. Every time she was offered a drink, coffee, a meal, she said yes. Not once did she offer to buy the dc so much as an icecream.
I sent birthday and Christmas gifts until her son was three. There was no thank you or reciprocation just messages via MIL about what was wrong with what had been sent.
When her father died, she decided not to attend the funeral because the upset and MIL's grief would be too much to make a short journey worthwhile.
All of her children have now dropped out. One is addicted to gaming.
Despite her social principles, she's never been shy of asking her capitalist bastard brother for a handout.
Thankfully she lives on the other side of the world and has only visited her parents/mother 4 times in 35 years. I have no time for her and suspect she'll be here faster than anyone can say "Jack Robinson" when her mother dies, to find out what her third adds up to.
She isn't nasty, she's just not my type and I dislike the laziness, and her can't be bovvered and woe is me attitude. I have swallowed "well, if you worked a bit harder, you wouldn’t be skint" so many times.
Sweet catharsis.