Despite being in the back of a police car, Jalen Rose didn't seem to understand he was getting arrested for DUI ... until the cop spelled it all out for him.
TMZ has obtained video of Jalen inside a cop car in Michigan on March 11 -- moments after he was tossed in the back for allegedy driving drunk.
In the video, the following exchange takes place between Jalen and the cop:
Jalen: "So what are we doing right now?"
Cop: "We're gonna go to the police station right now."
Jalen: "To do what?"
Cop: "You're under arrest."
Jalen: "For what, sir?"
Cop: "For drunk driving."
Jalen: "But I wasn't really drinking."
Cop: "Um, okay."
Earlier today, officials released the police report -- which shows Rose's blood alcohol level was over the legal limit at the time of his arrest.