The incident was filmed by a customer, and in the footage, staff at the Port Alberni ice cream chain can be seen arguing with the man about British Columbia's masking policy.
"It's not a BC policy," the man said. "BC policy says you have to observe exemptions."
After the man was unable to convince the Dairy Queen staff that he deserved an exemption to the mandate, he appeared to unzip his pants and relieve himself on the front counter.
"He's doing it!" a staff member can be heard yelling.
Upon finishing, the man called all the employees "psychopaths" and left.
Local police have not made an arrest and said the incident was a rarity.
"This is the first incident of this nature," said Royal Canadian Mounted Police Sgt. Chris Manseau. "I think people should just wear their masks and be safe and be polite."