When used to describe oneself, it is a comic expression used to indicate a unique and eccentric nature, i.e. one who does not follow the norm of life.
Certain people use this expression to be hurtful and condescending, while others enjoy being recognized as extraordinary.
A Window-Licker is a reference to a retard whom only posseses the ability to twist his/her head and lick uncontrollably. Then crossed with the hilarious image of one licking a window.
Can be used in a one phrase sentence I.E 'Lickie-Window!'
Harry trys to ink bomb a person 2 rows infront in school. He proceeds to launch it, missing, hitting ginger haired, cadet crazed form teacher.
Aaron: (retard sounds) Lickie-Window Harry!
Tom: Lawrence is such a Window-Licker! Look at him play cricket!