The forward, for reasons only known to him, decided to hack down a young supporter at what looked like some sort of open training session but the youngster was unbowed.
Rather than cry or squeal at his miss-treatment, he turned and flipped the Brazilian-cum-Spanish forward a one-fingered salute.
Having grown up playing street football, Costa is a fiery, temperamental, wind-up merchant prone to random acts of violence – and at 6'2", he is more than capable of dishing it out.
Here are just some of his misdemeanours:
Costa was slapped with a four-match ban from last season’s Europa League for this Streetfighter-style headbutt on an opponent.
He somehow evaded action for this incredible display of thuggery in a Liga derby with Real Madrid, spending the entire match using his head, feet, elbows and potty mouth to provoking Sergio Ramos and Pepe, both of whom have a temper. The worst bit of all comes when he elbows Ramos before spitting into his glove and flicking the phlegm at him (from 1:45 in the video).
His insult of choice is a widely-used Spanish expletive questioning the parentage of his rival, which can also kindly deliver in Portuguese if required. Indeed, he is so well-known for this phrase that opposition fans have taken to singing it at him in ironic tribute.
Player profile: Diego Costa
Height: 6’2” (1.88m)
Club: Atletico Madrid
Previous clubs: Braga, Penafiel (loan), Celta Vigo (loan), Albacete (loan), Valladolid, Rayo Vallecano
Fact: Only played street football until aged 16, when he was scouted by a local non-league club in Sao Paulo