basically a goober is just a kindhearted, rather oblivious goofball. it's term of endearment really. it comes from the ancient scottish verb "to goub", which has to do with doing a dance and smiling sheepishly while doing so, exposing the goubs in one's teeth.
"That John is such a goober," said Jane as John vector-danced* his Junior Prom away.
*footnote: the vector dance involves angling one's arms to form angles and vectors and pumping them back and forth to music. basically, it's geeky as hell. but completely sexy.