i don't get it.. in the last one why, 'Dad'?

In Japan gays can't marry but adult adoption is legal. So technically they are going to be father and son, but it's only on paper. That way they can be a family without the legal bind of marriage.

ahhh.. thankk youu

In addition to Laughing Wolf's correct assessment, the one yelling was sounding an awful lot like a father yelling at his useless son. LOL It was a perfect combination of moments for that response.