Well, I have tons of these but some of the funniest are from my Mother in law and her peers. They constantly nag me to cover my baby so she doesn't get sick. What's annoying about that is that my MIL has no problem bringing her other snotty nosed feverish grandchildren to my house, or near my baby...uhm, no THAT will make her sick!!!
One aunt also told me not to let my baby look in the mirror because it will stunt her growth! My mil asked me when my baby will get real milk. I just said, "she gets real milk, from me!" Then she apologized. hehe She's actually good about listening to me, but I have to watch her. She tried to give my 9mo a strawberry (which dd1 had a really bad reaction to before she was 2) but she didn't push, she just stopped. If I was her daughter she would have given to her anyway. haha They also asked me all the time when I was going to pierce my DD1's ears, I always told them we were going to do her nose first to match mommy, and that shut them up!
Today someone with a younger baby was telling me how small my baby is tiny (and she is only in the 5th percentile) and asked me if I drank coffee when I was pregnant! lol! My parents told me coffee would stunt my growth (tongue in cheek of course) so I drank as much as I could when I was younger...I wonder how tall I would have been without it because I am almost 6' now!
On the food front....I have a nephew who is cared for most often by his grandma, when she found out he had 4 cavities at 4 she said he "eats candy all day long!" Uh...in your care...too bad you can't stop him! Now he eats fruit snacks all day long...which his mom also said, "I can't buy the big boxes because he has to have at least 2 packs I can't stop him from eating them!" Uhm, ok...and hellooo, still candy.
This is not advice either but I recently saw a probably 18mo old on a leash thing...you know what I mean, and the parents were sitting next to him on the ground and letting him chugg their mountain dew. Kind of defeats the purpose of the leash, right? haha!!!