When an individual attempts to sound smart by using two synonyms after each other.
'Hence why' does not equate to 'that's why'.
Hence Why ≠ That's Why
"... global warming is becoming an increasingly accepted theory; hence why we are seeing a rise in environmental groups... " - said by relatively intelligent people who have a loose grasp of grammar.
"I spent all day in the sun; hence why I've got a tan" - intellectually challenged, yet attempting to prove their IQ fits within the norm.
An arrangement of these Japanese hiragana to create a face (he へ for the eyebrows, no の for the eyes, mo も for the nose, he へ again for a mouth, and can be surrounded by ji じ to outline the face)
へ へ
の の
も
へ
Sensei proceeded to draw the henohenomoheji face on the chalk board, for fun.