I think this has been said before but I'll say it again....cyclists riding at night with no rear &/or front lights, or any lights for that matter!! That goes for motorists as well.
Standard driving practice in Malaysia.
no helmets on motor-bike, 3-4 people on motorbike, kids standing up on car back-seats, no lights on cars, motorcycles, bikes, no baby-seat etc etc etc....so common hardly notice it now...