How does one rise above the pettiness of others

There are lot of people one meets and sees who seem so dignified and are always so polite and charming. I sometimes wonder how they would react if someone were to cheat them or bad mouth them. Would they still be able to remain calm when provoked.
The way you interact with people is dependant on the kind of people they themselves are. If someone is nice and friendly, you also loosen up and are nice and friendly. If someone is serious, you tend to be the same way with them. But when somebody's being mean, how do you react without becoming mean yourself! I mean, most of us are not saints.
And how does one deal with someone like your MIL who you cannot wish away from your life, but who is not so nice behind your back and in front of you! When I got married, I was this really naive person who thought everybody in her husbands family was wonderful, especially her MIL. But down the line, one learns otherwise! The problem is that she goes on pretending to be the great person she is... and I am left spending a lot of productive time on things like - I should have replied like this when she said that...next time she comes down, I will behave like this...and so on. I've become a lesser person thanks to her!

Lean babies are healthy babies

Kutti was a nice fat baby when she was born at 3.75kgs. I was mighty proud of myself for "my achievement". But after her 4th month, her weight gain started going down. I put it down to her body catching up with her genetic weight profile as I am small built myself and so is my husband. I continued nursing her exclusively despite the doc recommending solid food. We started solids at 6 months and madam turned out to be a very fussy eater and still is. She didn't gain weight at all for 3 months from 7th to 9th month. And then we started getting a little worried. Doc did blood and urine test and all turned out to be normal. Thereafter she started putting on a little weight thankfully - I used to take her to the grocer's shop and put her on the weighing machine to check her weight:) And now at almost 2, she is 10kgs and a little more. She is the same size as my neighbour's 1 year old! But atleast she is putting on a little weight each month. And I keep my fingers crossed:)
The funny thing is that whenever something is wrong with the baby, it is invariably the mother who is blamed. According to my MIL, she did not gain weight earlier on 'coz I am a vegetarian in a non-veg eating family and my breast milk is no good! And she would tell this in front of all and sundry! And that we (read my parents and myself who held her and rocked her to sleep when she was an infant) passed on too much of our body heat to her and hence she didn't gain weight. And I don't feed her nutritious food. And so on... And of course, my own doubts on whether I was doing a good job of being a mother.
But I'd like to believe that lean babies are healthy babies and grow up to be healthy adults.