Two men were walking past the house on Southfield Road in Almondbury, Huddersfield and one of them spat at the victim.
When he asked the suspect to clean it up, the man refused and threatened him with a knife.
No-one was injured and the men made off in the direction of Ings Road.
The first suspect is described as a white, aged 24 or 25, five feet, five inches tall with a goatee beard. He was wearing a silver fluorescent puffa type jacket and a beanie hat.
The second suspect is mixed race man, aged 24 or 25 with black hair and around six feet tall. He was wearing a black hoodie and grey trousers.
West Yorkshire Police is appealing for anyone who witnessed anything or have any information about the incident to come forward via Kirklees CID on 101 quoting crime reference 13180508944 or via the Force’s Live Chat facility www.westyorkshire.police.uk/101livechat. Information can also be passed anonymously to Crimestoppers on 0800555111.