To beat up. In its transitive form, to assault someone violently (он его так упиздил, что тот встать не мог — “he beat the absolute shit out of him so hard he couldn’t stand up”).
Удивила мягкость товарищей милиционеров… могли и упиздить с полным на то правом.
The softness of the comrades policemen surprised me… they would have been entitled to beat the living shit out of him.
(nail helgi @ ЖЖ, 04/2011)
