This oxymoron is used to tell someone to blend in or pretend to be normal.
Act Naturally
This (admittedly not literary) convention opens nearly every Star Wars movie.
"A long time ago, in a galaxy far, far away" / The Title Crawl
A phrase used when something is both good and bad.
Bittersweet
This character trope involves a person who bestows wisdom upon the protagonist, but often tragically dies.
Old man / Old wizard / Valid example
One can receive assistance at this airline's desk.
The Delta Help Desk
A trope used with an attractive neighbor, often from a boy's perspective.
The girl next door
This sport brand for pain relief has its name as an oxymoron.
Icy Hot
This comic relief is often seen beside a heroic protagonist.
Witty side character
The definition of an oxymoron
A combination of opposites; the union of contradictory terms
The definition of convention
A device of style or subject matter so often used that it becomes a recognized means of expression. I.e. a cliche, device, or trope that acts as a defining feature of a genre.