Let me break your question into separate pieces... So first I'll explain you about this part :-
I didn't read all the things from vedas and I dont have even enough time to search the proof.
Here, this is the exact reason why not only him but most of the active users asks for a scripture reference rather than a proof. The reason why we ask scripture references because as you said, Hinduism is a vast religion, with thousands of beliefs and too many version of the same stories. Inorder to maintain the quality state on the site and the content authenticity we request our users to backup their answers either with scripture reference or you can also link your post to a website which provides similar information.
Now am saying link to the site, so please don't copy paste it straight away. As you said that you didn't read all the things from Vedas hence you should either ask questions or you should start learning about vedas, if you think you are professional or too good in Hinduism then you should consider answering but if you are a learning user, surely you can answer but please provide some references to backup your claims, it helps users to refer answers.
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Coming to and If I wrote something in Hindi then what's wrong? Hindu is written in Sanskrit and Hindi is daughter of Sanskrit.
Well, there is no issue if you write a part of your answer in Hindi or Sanskrit BUT we are on the internet, the site is intended to target not only Hindus but anyone who is interested in Hinduism or its topics so think of an American user reading Hindi/Sanskrit and he wont get a bit of what you are writing in your answer so answering should be in English, if you want to share a Sanskrit snippet from our scriptures, it is completely fine but make sure you explain them in English as well..
Kindly avoid such users who tries to being the moderator and comments over each answer.
He is not a moderator, trying to help users or keeping the site doesn't mean that he acts as a moderator but you can say that he is helping to keep the site clean and on topic instead. If he down votes any of your answers, take necessary action, provide references and he will retract his votes back.
I am keeping a check on the voting patterns of most of the active users so never think that anyones playing unfair here. If you feel fishy about votes then instead of raising a question on meta you can contact a moderator by flagging any random post and writing a message to check the vote patterns.
After today's incident he down voted my answers repeatedly. Please do something positive for this kind of activity
As I said, am keeping a check on users activity, if we think that the user is playing unfair we will surely revert their votes back but they are not out of envy but with a reason. Also you cannot be sure that he has voted all the down votes you've scored.