How do I develop a thicker skin?

On monday i had a rare opportunity to take my son to his 'top tots' class (I had a day of leave, our nanny usually takes him).
I was really looking forward to it and I guess, to showing the other mommies, that yes, little Ben does have a mommy who loves him (its just she has to work, so cant take him to classes).
Im still a bit emotional about what happened... perhaps its the pregnancy hormones, or perhaps i just need to develop a thicker skin.

first of all, only one of the mommies said one word to me. all the others chose to ignore me other than throw the occassional dirty look in my direction.
you see, my sweet, kind little Ben over the last few weeks has morphed into quite an aggressive little chap. he doesnt seek out confrontation, but if you come between him and anything he wants (toy, car etc) he pushes, pinches and yes, an occassional bite. I was completely shocked. Ive never seen him like that. the leader of the group reassured me that its just frustration during this difficult time of a toddlers life. she said she had seen way worse.

the other ladies however, were behaving like my child was the son of satan.
which really broke my heart.
you see, i know the real Ben, the happy, laid back, charming, lovable Ben.
and all they chose to see was the 'bully ben'. as if their children have never shoved another child over to get to a toy.
as if theirs are angels sent from heaven who'd never kick, shout or be otherwise unreasonable.
In the numerous times that Ben has been knocked over etc by other toddlers, I have never ever made the mother of the transgressor feel as bad as these women made me feel. Ive always with good grace said 'toddlers will be be toddlers' while intervening to lessen the damage.

I know this probably shouldnt bother me as much as it does... but it does! and I cant seem to get it out of my mind.
we've since removed Ben from the class, because after direct questioning it turns out that these ladies have been equally mean to my nanny. She didnt say a word to me, probably because she was afraid to.

I know Ben turns into a little monster when he cant have what he wants. But he's also completely wonderful, soft, gentle, shy and thoughtful. and it kills me that this jury of women dont see that. I guess, Im expecting too much and really do need to develop a thicker skin. But it feels like my little boy has been 'wronged' and he isnt even 2 yet.