'Vampire Diaries' Star Zach Roerig Busted for DUI, Allegedly Peed in Jail Cell

"The Vampire Diaries" star Zach Roerig was allegedly a mess in more ways than one over Memorial Day weekend -- when he got busted for DUI, cops say he urinated in his jail cell.

Law enforcement sources tell TMZ ... Zach was busted Sunday around 2:30 AM in Montpelier, Ohio. Police tell us, officers noticed Zach's pickup truck did not have a front license plate, so they pulled him over.

Our sources say when the officer went up to the driver's side window, cops noticed Zach's slurred speech and bloodshot eyes and say he reeked of booze.

We're told police conducted several field sobriety tests during which Zach told the officer, "This is very hard, I can't do this when I'm f***ing ..." and his voice trailed off. The cop asked what he meant, and we're told Zach replied, "When I can't have a beer."

Cops arrested Zach for misdemeanor DUI. When they took him to the station, our sources say he was placed in a holding cell, where he ended up peeing. Long night.