Define Half A Bubble Off Center Meaning

HALF A BUBBLE OFF CENTER
not all there, mentally speaking. A couple of sentences short of a paragraph, a few shards of pottery short of a full anthropological theory, a few wafers short of a communion, one's belt doesn't go through all of the loops, one's driveway doesn't quite make it to the road...I THINK YA GET THE PICTURE!

That loony sumbitch is definitely half a bubble off center -- he's crazier than a pet coon!
By Elsey