The happiest man on earth would be able to use the Mirror of Erised like a normal mirror, that is, he would look into it and see himself exactly as he is. Does that help?
The happiest man on earth ...
Quotes from the same author
Raindrops the size of bullets thundered on the castle windows for days on end; the lake rose, the flower beds turned into muddy streams, and Hagrid’s pumpkins swelled to the size of garden sheds.
He didn't realize that love as powerful as your mother's for you leaves its own mark.
I am prouder of my years as a single mother than of any other part of my life.
So why in the name of Merlin’s saggy left — Don’t talk to your mother like that.
Hermione drew herself to her full height; her eyes were narrowed and her hair seemed to crackle with electricity. "No," she said, her voice quivering with anger, "but I will write to your mother.