Fabius finished top of the class in his centurion training, his fit physique is the very model of what a good Roman soldier should be.
After training he was assigned to be the body guard of the Legionis. After a few months of not having to do much fighting, eating extravagantly in the palace and multiple jugs of wine a day, there was a notable change in his physical appearance.
To the palace guards the change was gradual and went unnoticed but to his friends Gaius and Marcus who had just come back from the campaigns in the north, the change was very noticeable. They took great pleasure in teasing their friend about his soft life and how well he adapted to it, their own abs clearly visible through their armour. Gaius grabbed Fabius' soft, pale belly trying to see if there was anything left of his once clearly visible abs with Marcus laughing as he poked and prodded his friends gut.
From that day Fabius was known as Flabius