Obvious answer is: no, it's not reasonable to be mean to your parents in law.
I have to see my PIL fairly regularly. They've been in my life for 15 years and they've never really been my kind of people. They're very loud, negative, mean spirited and judgemental, constantly talking over everyone and full of bigoted opinions. When i was younger, I'd pick them up on a couple of things but as I've got older, I no longer really see the point and instead am quite indifferent, nodding neutrally at whatever they say.
I find it really difficult to be nice to them. The nearest thing I can think of comparing it to is when you're shy and can't simply just 'speak up'.
I don't want it to be like this. I'd like for us to be able to get on. Is there a way of getting past these feelings? I've really tried making an effort over the years but recently I've found it so much harder to muster up kindness towards them.