Oxymoron and Irony: Opposites Attract Each Other and Emphasis Is Born

An oxymoron is a phrase that seems self-contradictory or incompatible with reality. By juxtaposing two opposite words (that is A + Not A as in "living dead"), writers seek to achieve dramatic contradiction or vivid imagery. 
As the Latin etymology of the word shows--oxy (“pointed or sharp”) + moron (“foolish or dull”)--"oxymoron" is the best example of its kind. 

Eloquent silence
Deafening silence 
“And faith unfaithful kept him falsely true.”
Irregular patterns
Organized chaos 
Serious jokes
Dry drunk
Quiet riot 
Icy hot
Bitter sweet
Idiot savant (= wise fool) 
Electric candles
Plastic glass 
Profoundly shallow 
Terribly nice
White gold
Grow smaller
​Clearly confused
Obviously oblivious 
Civil War 

​Verbal irony:
as soft as concrete

as clear as mud

as pleasant as a root canal

"as pleasant and relaxed as a coiled rattlesnake" (Kurt Vonnegut from Breakfast of Champions)

Situational irony: incongruity between expectations of something to happen and what actually happens

​Dramatic irony allows the spectator an item of information that at least one of the characters in the narrative is unaware of.