Forget hotel bars and spanish steps area. Real roman nightlife happens in san lorenzo and pigneto districts.

San lorenzo: studentetesco does proper cocktails €6-8. Crowd is university mixed with young professionals. Gets packed after midnight. Know what you want before ordering.

Pigneto: necci dal 1924 for aperitivo then move to barrio maravillas for late night. Former is classic italian bar culture. Latter is more international crowd.

Trastevere looks good but its tourist central after 10pm. Locals fled years ago except for freni e frizioni which somehow maintains authenticity.

Romans start late. 11pm is early. Midnight is when things begin. Pace accordingly or you'll drink alone.