Chatham-Kent police tell us the incident happened about 5:30 in the afternoon at a business on Talbot St, East in Blenheim.
The victim, a 54 year old man was waiting in line, when witnesses say the younger man lunged at him with a knife and stabbed him in the abdomen.
Fortunately it was a superficial wound.
The 21 year old fled the scene, but he was later arrested and charged with assault with a weapon, and weapons dangerous.
He has been remanded in custody pending a court appearance on Tuesday.