DS has 2 webbed toes on each foot that don't affect him at all:
"Are you going to have him operated on?" - ahem, NO!

DS also is quite pigeon toed.
"You should have that looked at" - My father is an orthopaedic surgeon, he examined him and said that his hips are slightly tilted, so he needs to walk pigeon footed so as not to damage his hip joint. If you try and force him to walk "normally" (which is what used to get done) he will wear his joint down and have lots of problems later. In 95% of cases, his hip will become normal through growing, then he will naturally adjust the way he walks. If not, you can deal with that at a later stage
"I think you should get a second opinion"
Jeez, if I trust ANYBODY to have my son's best interest at heart then it is my father who I know is someone who constantly reads and educates himself on new developments on his field of expertise.

And then the usual:
Are you STILL breastfeeding? When are you going to wean? - Well, I don't know actually, when either he or I feel like we don't want to anymore.
What? He sleeps in YOUR bed? What does your husband think of that? - He doesn't mind.
He's such a mummy's boy - Well, isn't that normal? He's only 2! And I used to get that comment before he turned 1!
To my skinny daughter who doesn't eat much: "Don't eat xyz, it will make you fat" - actually, I don't want that word used around my children at all.
"Don't put salt on that, it will make you sick" - coming from my in laws who cook the blandest foods.
"You have such a bad cough, ask mummy to give you some medicine" - after a single little cough. ahhh, I don't do cough syrup!!!
Basically anything from someone else that pushes their thoughts on nutrition or medication onto my children.