since when can anyone vote his answer as the best one????

If the asker doesn't pick a best answer to a question, it goes into 'voting' and anyone can vote for the Best Answer. There's nothing to stop an answerer from voting for his or her own answer.

There are thousands of unresolved questions out there. I vote my daily limit each day, do you?

:o)

When it goes into voting

I'm going to pick mine as the best. What was the question?