Being as intoxicated as he was, McNulty was probably angry that he didn't total his car more seriously, IE, he was angry at how his night had been going & wanted to take it out on his car. So he took another shot & did more damage.
Despite being hammered, McNulty cannot accept that he has failed to negotiate the bend in the road. He gets out, checks the angles, reverses and does it again. McNulty refuses to entertain the fact that it he could fail at a task. These are the roots of his deep-seated personality problems.