Most people would not want their favorite jacket to be ruined by something as offputting and dirty as vomit and so this it cannot be the best thing that happened this weekend.
Consider the statement "My buddy drank way too much at a party and puked all over my favorite jacket.". Based on this "The best thing that happened this weekend was when my buddy vomited all over my favorite jacket." a true statement? Yes, no, or I don't know?