The fact that its 3am in a residential area on a weekday. How do you know they arent durka durkas waiting for the next nosy asshole to blow up the bomb they're sitting on?
When you don't know, call the people you pay to keep you safe; if the men with guns who are legally allowed to shoot people play it safe, pull their guns, and have the guys exit the car one by one, they might be on to something with this whole "caution before bravado" thing.