A Mission man learned — the hard way — yesterday afternoon that just because someone you met at a bar offers to smoke weed with you, their intentions are not necessarily benign.

According to the San Francisco Police Department, a 51-year-old man was drinking at a Mission District bar at 3 p.m. Sunday when he made a group of new friends: An assembly of four or five men between the ages of 18-25.

When the younger men invited him to join them in smoking some weed, they retired to an alley somewhere between Valencia Street and San Jose Avenue, police say. That's when the younger men attacked their elder, and one of them stabbed him with a knife, leaving him with a laceration to his arm.

Police say that following the stabbing, the victim walked to hospital for treatment of his injuries, but was so intoxicated that he "does not know how he got to the hospital."

The man's injuries are not considered life-threatening, and he's expected to make a full recovery. Police did not have any additional information on the suspects, but says that no arrests have been made.