I did yesterday. Pasted below and clarified a bit more.

Example: If I startle someone and cause them to have a heart attack then visit this person at the hospital they may say "you literally scared me half to death."

When the same statement is said without "literally" the statement may be taken metaphorically.

Another may be "The energy prices in Europe may bring them to their knees." In this case bringing the Europeans to their knees may be taken metaphorically as in to the edge of starvation, or to the brink of financial pain etc. In this case they are not actually getting on their knees but instead the term is bringing attention to the desperate circumstance the Europeans may face but doesn't explicitly indicate the action of kneeling.

Add "literally" and the reader will understand a literal rather than metaphorical meaning as in bring them to their knees in prayer or to beg for releif. "The energy prices in Europe may literally bring them to their knees." In this scenario the inference is still that the Europeans will face desperation, financial pain and starvation but without the ambiguous metaphor.

But again "literally" is deployed in order to further zero in on a meaning of a term and in this case a metaphor. In your case "retarded" does not need clarification or defining but what I think you were trying to drive was amplification or to give the word more impact. That's why I suggested "very" rather than "literally." "Very" would not only tell the reader they are retarded, which is bad enough of an insult, but your driving it home even further by saying that they are worse than retarded and letting the reader boil in their imagination. What's "very retarded" pfff.. Who fucking knows but it's worse in fact so bad they haven't even come up with a word to describe it.

When insulting someone your best weapon is their own mind. The tool one would deploy to get into their mind is your words. The twist of the knife and cherry on top within your insult is the careful precision and placement of words and language. Every word chosen need not be wasted and must strike like a smiths sledge hammer. Cut out all fat, use your intellect and above all strengthen your understanding of logic.

Once you begin to perfect your language, logic and deployment thereof I would argue you would rarely if ever have the use for words "retarded" and "literally." Your choice of words would bleed out your opponent, your logical argumentative skills and deployment would serve to insult. If done correctly you may have convinced a few of those that disagree to battle alongside rather than against.