Taking normal, everyday things and making them extreme. Slang term introduced into the Greenville, OH region. Thought to have been introduced by people who would do unnecessarily extreme things like rip sleeves off of shirts, wear sleeveless shirts in cold weather, and drink highly caffeinated energy drinks.
The douchebag had to "Sheltonize" a perfectly good t-shirt by cutting the sleeves off, so he could be a sweet broseph and wear it to the gym.
The guys at the gym "sheltonized" their flow session by drinking AMP before hand.