I live with DH a long way from my parents but near to his parents. A few months ago my parents came to visit and the in-laws cooked lunch for them at their house.
When my parents knew they were due to come up again they wanted to return the in-laws hospitality. Obviously they couldn't cook them lunch so instead they said that they would take me and DH and the in-laws out for lunch to say "thank you".
This was explained to MIL and she said she would book a restaurant. However when me and my parents and DH turned up PILs were there with DH's two brothers (who are both in their twenties, working, etc) and it was clear that MIL expected my parents to pay for the 2 BILs too!
Now my parents are not wealthy and I could see my mum was mortified that she was expected to pay for 2 adult men's meals (who she hardly even knows). Therefore at the end of the meal it was a bit awkward as I said somthing about the BILS should pay and the PILS were very offish about this and one BIL even made a very loud comment that it was "funny to have to pay when you've been invited out" - he wasn't even invited!!!
Please tell me I'm not BU to think that PILs were really rude to do this!