Spencer Pratt Busted for Mud Flaps

Spencer Pratt is a dirty mud-slinger -- and according to the police, dude needs to fix the problem stat.

Spencer Pratt: Click to watch
Heidi Montag's other half was pulled over by the LAPD last night because his monster truck lacked mud flaps -- which are required on massive rides so mud and debris doesn't get shot back at other vehicles.

During the stop -- in which Spencer invited the cops to go clubbing with him -- the officers nailed Spencer for not having proof of insurance.

Spencer was eventually sent on his way with merely a fix-it ticket, which requires him to get his vehicle up to code by March 15.