Samsung Silent Mode
To activate silent mode on a Samsung phone, press and hold the # key (hash, pound). To deactivate it, do the same again.
I found this out after telling my Samsung-loving girlfriend that my Samsung phone sucked because it didn’t have profiles like my beloved old Nokia - at which point she picked up my mobile, pressed #, and rolled her eyes.
“Silent Mode activated” 
Next time I’ll RTFM.
