I know, I know, I'm such a cliche, but my MiL just irritates me so much. Every single time she comes round to the house she asks if she needs to take her boots off and then tuts and says things like "my boots aren't even dirty" when I say "yes please". The ironic thing is she always says "shoes off" when we go to hers, even when we're obviously in the porch about to take them off.
She also complains every visit about how low our settees are (they're just normal settees, not particularly low) and then gets a cushion or two and sits on them on top of the settee cushion.
She also likes to comment on our parenting by saying things in judgemental tones about how she never did whatever it is when her kids were growing up. We went for a meal when DD was a baby and when DP took DD for a nappy change she said "oh I never expected (insert DP's father's name) to change a nappy when the boys were growing up. Not when they're working full time."
So AIBU to let these things grind my gears so much....