Lyric discussion by skacore_dude 

Cover art for Mercy Me lyrics by Alkaline Trio

It's just about how he wants to get on with life, but it's not going to plan and hes 'lost' and on the verge of going insane.

SoConstantine... it is metaphorical, becuase he's on about 'driving' himself insane, and he's implying that he's could easily be 'driven' insane because the petrol tank in his car is filled.