.:Mintcoin:.

lazy.
He was visiting his dying grandpa's house when he found a collection of rusting bits. He decided to shine them up, (since he's such a clean freak) and found that underneath the rust were very old, very valuable coins. He decided to take them home, and began collecting as many old bits as possible. Eventually his parents gave him his first mint condition bit (a bit older than his grandfather) and his cutie mark appeared.

Mintcoin was born as Filthy Rich's second child (to another mare), making him Diamond Tiara's younger half-brother. She never really like him, mainly because he was the child of a mare she didn't like, and was always confused by his minty green hair. No one in their family had that colour (I'm Canadian, shuddap) hair.
Ponies automatically thought he was a snob, because of his family. The only one who he could talk to was his grandpa on his late mother's side. He was a gentle pony, but died soon after Mint turned 5 (on Hearth's Warming Eve, may I add). From then on, since no pony seemed to listen, nor like him, he became cold and ignored most ponies.
To release his anger he began cleaning almost every surface he could find (although he was already clean as it was). Eventually it became his go-to stress reliever.
Now he basically ignores school, though manages to get the best scores, and spends most of his time at home shining his bit collection.

Approved!