Squealing brakes - the old Mafac RACERs! I used to set them up so moderate stops weren't too loud but if a car cut me off (Boston city traffic) I'd hit the front extra hard. Every pedestrian within a block would turn and look at me. I'd point to the driver. Eyes follow my point. Driver gets awakened from his stupor by the squeal, looks up - and everybody is looking at him! Driver slinks off like a guilty cat. It was rather fun and well worth the effort to dial in the squeal.