'Percy' is short form for personal, but has been injected into the definition of 'legit, good shit and unreal' (usually pertaining to drugs).
This is because drug dealers keep the best stuff for themselves, a drug dealer's 'percy' weed is the best weed they have. Really baked stoners deciced to confuse everyone by calling good weed percy, cause they are fucked.
"That fat hoe has massive rolls but shes got a fine, percy ghetto booty"
"I have the most percy chronic in all of the greater North America area"