Originally originating from Howard Dean's Scream/Dave Chapelle's Parody "Byah" then famous streamer "Sodapoppin/Chance Morris" changed the B to a P.
Pyah as described by Sodapoppin has no significant meaning, but it was used after he beat noobs in arena. Can also be used in awkward situations to slip away.
Pyah means go fuck yourself. Usually said after someone makes a stupid remark or is said to someone just being a retard. Is said before walking away without giving a fuck.