Hoy is rather rude if by itself. When speaking to someone you know, the intonation matters a lot and the manner it is delivered. Usually, when speaking to someone you know, you say it in a phase which is, hoy, kamusta? but it is pronounce as uy, kamusta? To someone you don't know or is older, you say " Magandang araw po, mawalang galang na po " which means good day, please excuse my intrusiveness.