what stealthsquiggle said
One meeting early on in our relationship (13 yrs ago) all very civil but all very unrelaxed. My parents don't have great social skills!
Then when dd born there was pressure from MIL (actually had often been pressure but I'd resisted) to arrange another meet. All went fine - for once the baby smoothed the social situation.
My parents have moved and just about to arrange a holiday with ILs nearby. Trying not get worked up about how the inevitable meet up will go!
I know dp gets upset when I mention ILs to my parents. Possibly I do roll my eyes occasionally! But if I can't do that with my parents who can I do it with?
I know one couple where both sets of parents have become best of friends.