We don't get on with MIL - I posted just the other day about her inviting herself for lunch when DH has just had an op and we're a bit frazzled. A cucumber was involved 
I was going to respond to another thread about comparing gcs unfavourably but once I'd typed it I realised it would be a total hijack.
Anyway the situation is that d niece has just been born and comparisons have duly begun... 'Ooooh,, maybe I shouldn't say this but... She's so laid back. I've never seen any baby so laid back.' That might not sound like much but it's her total modus operandi and I can just see it coming - she hates everything we do with DD - she's very old school and thinks we should mainly be telling DD off, preferably with some smacking. She's made the 'laid hadn't comment four times now - always preceded by I shouldn't say this' or something similar.
We don't care really, we get on well with dBIL and SIL and I suspect she's chosen this route because if she tried the shit she pulled with us when DD was born on dBIL he'd cut her off no question. But some wise MN phrases on how to nip this in the bud would be v handy.