Bangkok after dark is not one strip. Yaowarat centres an evening on food, the Chao Phraya on river views, and Silom or Sukhumvit on denser bar and club choices. Pick one district so the night is not spent in traffic.
Yaowarat is strongest as a walking food circuit with temples, old trading streets and busy roadside dining around it. The riverside works better for a slower dinner, ferry view or hotel bar, but crossings and boat services may end before the city does.
Current venue hours and dress rules change. Confirm them directly, especially for rooftops, ticketed events and places inside hotels.
Sukhumvit and Silom concentrate many late venues near rail corridors, though the final walk or ride still matters. Save the hotel address in Thai and decide on rail, taxi or app transport before drinking.
Keep your own drink in view and do not leave a companion alone when impaired. Tourist Police can assist in multiple languages on 1155; police emergencies use 191 and medical emergencies 1669.