What is "B A Y"?

Weekend time. I was playing with Mrunmay, one of his games - 3 letter words. Basically there are some paper strips having one letter printed on it and then there's a letter dispenser, which dispenses 2 letters at a time. The game is to make up a word with those two letters and one of the paper strips.

It's too early for Mrunmay to know the spellings and obviously the job of finding out matching spellings was with me. After every round, I was telling him the meaning of the word formed, in the form of question / answers. Like "Do you know this word?", "Do you know it's meaning?" and wherever required giving him examples and/or translations.

After few rounds, the dispenser gave us two letters: "B" and "A". The only possible combination left was the word "BAY". I started asking him the meaning...
Me: "Do you know what is BAY?"
Mrunmay: "Bay??"
Me: "Yeah.. do you know what is the meaning of Bay?"...
I was hoping that he'll relate it to "Bay of Bengal" which he know from the map.

Suddenly his eyes sparkled and he started singing:
प्यार दीवाना होता है मस्ताना होता है ...
I was totally puzzled. I could very well see he was singing it on purpose and wasn't a random song. He has picked up this song for last few days and once in a while he keeps on singing it. But I was absolutely clueless why is he singing it NOW???? He continued..

हर खुशीसे हर गमसे बेगाना होता है।
with twinkling eyes, he said - बाबा - "बेगाना"... "बे"... बाबा... "बे" :)

And there was a burst of laughter in the room!!