Today I just logged to magento.stackexchange.com and shocked to see that my Profile Pic is changed and Reputation point is decreased (-125), saying −xx User was removed
Can any one say OR explain, what's happened to my profile ?
All I can tell you is that your -125 points come from the fact that a user that upvoted your questions/answers got deleted. Read more about this here.
I have no idea what happened to your avatar.
I only see in the activity report 2 avatar changes from May 30.
Maybe you changed the avatar on stackoverflow.com and you also clicked to change it on every other site in the stackexchange network.