This is the 4919th most frequent Polish word.
pijani
"Drunk."
The word "pijani" here is used as an adjective to describe "kierowcy" (drivers), indicating their state of intoxication.
Pijani kierowcy są zagrożeniem na drodze.
Drunk drivers are a danger on the road.
The word "pijanych" here is the accusative plural form functioning as an adjective modifying "ludzi" (people).
Wczoraj widziałem kilku pijanych ludzi w parku.
Yesterday, I saw a few drunk people in the park.
The word "pijani" here works as a predicate adjective, describing the subject's state as they performed the action of returning home.