A famous (or infamous) neighborhood known for go-go bars, but also has good restaurants, night market, and nightlife.
Patpong is Bangkok's red-light district with legal adult entertainment venues; also has bars, restaurants, shopping.
Touristy, energetic, not dangerous but crowded and sometimes rowdy; sex workers and bar girls everywhere; not for everyone.
If curious about Bangkok's nightlife; good restaurants and bars that aren't overtly adult-oriented; Silom night market is right there.
Generally safe; just use common sense, watch drinks, respect people working there; avoid if uncomfortable with sex work.